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SubjectRe: [PATCH 01/25] vfs: syscall: Add fsinfo() to query filesystem information [ver #14]
On Mon, Jun 24, 2019 at 03:08:54PM +0100, David Howells wrote:
> Add a system call to allow filesystem information to be queried. A request
> value can be given to indicate the desired attribute. Support is provided
> for enumerating multi-value attributes.
>
> ===============
> NEW SYSTEM CALL
> ===============
>
> The new system call looks like:
>
> int ret = fsinfo(int dfd,
> const char *filename,
> const struct fsinfo_params *params,
> void *buffer,
> size_t buf_size);
>
> The params parameter optionally points to a block of parameters:
>
> struct fsinfo_params {
> __u32 at_flags;
> __u32 request;
> __u32 Nth;
> __u32 Mth;
> __u32 __reserved[6];
> };
>
> If params is NULL, it is assumed params->request should be
> fsinfo_attr_statfs, params->Nth should be 0, params->Mth should be 0 and
> params->at_flags should be 0.
>
> If params is given, all of params->__reserved[] must be 0.
>
> dfd, filename and params->at_flags indicate the file to query. There is no
> equivalent of lstat() as that can be emulated with fsinfo() by setting
> AT_SYMLINK_NOFOLLOW in params->at_flags. There is also no equivalent of
> fstat() as that can be emulated by passing a NULL filename to fsinfo() with
> the fd of interest in dfd. AT_NO_AUTOMOUNT can also be used to an allow
> automount point to be queried without triggering it.
>
> params->request indicates the attribute/attributes to be queried. This can
> be one of:
>
> FSINFO_ATTR_STATFS - statfs-style info
> FSINFO_ATTR_FSINFO - Information about fsinfo()
> FSINFO_ATTR_IDS - Filesystem IDs
> FSINFO_ATTR_LIMITS - Filesystem limits
> FSINFO_ATTR_SUPPORTS - What's supported in statx(), IOC flags
> FSINFO_ATTR_CAPABILITIES - Filesystem capabilities
> FSINFO_ATTR_TIMESTAMP_INFO - Inode timestamp info
> FSINFO_ATTR_VOLUME_ID - Volume ID (string)
> FSINFO_ATTR_VOLUME_UUID - Volume UUID
> FSINFO_ATTR_VOLUME_NAME - Volume name (string)
> FSINFO_ATTR_NAME_ENCODING - Filename encoding (string)
> FSINFO_ATTR_NAME_CODEPAGE - Filename codepage (string)
>
> Some attributes (such as the servers backing a network filesystem) can have
> multiple values. These can be enumerated by setting params->Nth and
> params->Mth to 0, 1, ... until ENODATA is returned.
>
> buffer and buf_size point to the reply buffer. The buffer is filled up to
> the specified size, even if this means truncating the reply. The full size
> of the reply is returned. In future versions, this will allow extra fields
> to be tacked on to the end of the reply, but anyone not expecting them will
> only get the subset they're expecting. If either buffer of buf_size are 0,
> no copy will take place and the data size will be returned.
>
> At the moment, this will only work on x86_64 and i386 as it requires the
> system call to be wired up.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: linux-api@vger.kernel.org
> ---
>
> arch/x86/entry/syscalls/syscall_32.tbl | 1
> arch/x86/entry/syscalls/syscall_64.tbl | 1
> fs/Kconfig | 7
> fs/Makefile | 1
> fs/fsinfo.c | 537 +++++++++++++++++++++++++++++++
> include/linux/fs.h | 5
> include/linux/fsinfo.h | 66 ++++
> include/linux/syscalls.h | 4
> include/uapi/asm-generic/unistd.h | 4
> include/uapi/linux/fsinfo.h | 219 +++++++++++++
> kernel/sys_ni.c | 1
> samples/vfs/Makefile | 4
> samples/vfs/test-fsinfo.c | 551 ++++++++++++++++++++++++++++++++
> 13 files changed, 1400 insertions(+), 1 deletion(-)
> create mode 100644 fs/fsinfo.c
> create mode 100644 include/linux/fsinfo.h
> create mode 100644 include/uapi/linux/fsinfo.h
> create mode 100644 samples/vfs/test-fsinfo.c
>
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index ad968b7bac72..03decae51513 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -438,3 +438,4 @@
> 431 i386 fsconfig sys_fsconfig __ia32_sys_fsconfig
> 432 i386 fsmount sys_fsmount __ia32_sys_fsmount
> 433 i386 fspick sys_fspick __ia32_sys_fspick
> +434 i386 fsinfo sys_fsinfo __ia32_sys_fsinfo
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index b4e6f9e6204a..ea63df9a1020 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -355,6 +355,7 @@
> 431 common fsconfig __x64_sys_fsconfig
> 432 common fsmount __x64_sys_fsmount
> 433 common fspick __x64_sys_fspick
> +434 common fsinfo __x64_sys_fsinfo
>
> #
> # x32-specific system call numbers start at 512 to avoid cache impact
> diff --git a/fs/Kconfig b/fs/Kconfig
> index cbbffc8b9ef5..9e7d2f2c0111 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -15,6 +15,13 @@ config VALIDATE_FS_PARSER
> Enable this to perform validation of the parameter description for a
> filesystem when it is registered.
>
> +config FSINFO
> + bool "Enable the fsinfo() system call"
> + help
> + Enable the file system information querying system call to allow
> + comprehensive information to be retrieved about a filesystem,
> + superblock or mount object.
> +
> if BLOCK
>
> config FS_IOMAP
> diff --git a/fs/Makefile b/fs/Makefile
> index c9aea23aba56..26eaeae4b9a1 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -53,6 +53,7 @@ obj-$(CONFIG_SYSCTL) += drop_caches.o
>
> obj-$(CONFIG_FHANDLE) += fhandle.o
> obj-$(CONFIG_FS_IOMAP) += iomap.o
> +obj-$(CONFIG_FSINFO) += fsinfo.o
>
> obj-y += quota/
>
> diff --git a/fs/fsinfo.c b/fs/fsinfo.c
> new file mode 100644
> index 000000000000..49b46f96dda3
> --- /dev/null
> +++ b/fs/fsinfo.c
> @@ -0,0 +1,537 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/syscalls.h>
> +#include <linux/fs.h>
> +#include <linux/file.h>
> +#include <linux/mount.h>
> +#include <linux/namei.h>
> +#include <linux/statfs.h>
> +#include <linux/security.h>
> +#include <linux/uaccess.h>
> +#include <linux/fsinfo.h>
> +#include <uapi/linux/mount.h>
> +#include "internal.h"
> +
> +static u32 calc_mount_attrs(u32 mnt_flags)
> +{
> + u32 attrs = 0;
> +
> + if (mnt_flags & MNT_READONLY)
> + attrs |= MOUNT_ATTR_RDONLY;
> + if (mnt_flags & MNT_NOSUID)
> + attrs |= MOUNT_ATTR_NOSUID;
> + if (mnt_flags & MNT_NODEV)
> + attrs |= MOUNT_ATTR_NODEV;
> + if (mnt_flags & MNT_NOEXEC)
> + attrs |= MOUNT_ATTR_NOEXEC;
> + if (mnt_flags & MNT_NODIRATIME)
> + attrs |= MOUNT_ATTR_NODIRATIME;
> +
> + if (mnt_flags & MNT_NOATIME)
> + attrs |= MOUNT_ATTR_NOATIME;
> + else if (mnt_flags & MNT_RELATIME)
> + attrs |= MOUNT_ATTR_RELATIME;
> + else
> + attrs |= MOUNT_ATTR_STRICTATIME;
> + return attrs;
> +}
> +
> +/*
> + * Get basic filesystem stats from statfs.
> + */
> +static int fsinfo_generic_statfs(struct path *path, struct fsinfo_statfs *p)
> +{
> + struct kstatfs buf;
> + int ret;
> +
> + ret = vfs_statfs(path, &buf);
> + if (ret < 0)
> + return ret;
> +
> + p->f_blocks.hi = 0;
> + p->f_blocks.lo = buf.f_blocks;
> + p->f_bfree.hi = 0;
> + p->f_bfree.lo = buf.f_bfree;
> + p->f_bavail.hi = 0;
> + p->f_bavail.lo = buf.f_bavail;
> + p->f_files.hi = 0;
> + p->f_files.lo = buf.f_files;
> + p->f_ffree.hi = 0;
> + p->f_ffree.lo = buf.f_ffree;
> + p->f_favail.hi = 0;
> + p->f_favail.lo = buf.f_ffree;
> + p->f_bsize = buf.f_bsize;
> + p->f_frsize = buf.f_frsize;
> +
> + p->mnt_attrs = calc_mount_attrs(path->mnt->mnt_flags);
> + return sizeof(*p);

Hm, the discrepancy between the function signature returning int and
the sizeof operator most likely being size_t is bothering me. It
probably doesn't matter but maybe we can avoid that.

> +}
> +
> +static int fsinfo_generic_ids(struct path *path, struct fsinfo_ids *p)
> +{
> + struct super_block *sb;
> + struct kstatfs buf;
> + int ret;
> +
> + ret = vfs_statfs(path, &buf);
> + if (ret < 0 && ret != -ENOSYS)
> + return ret;
> +
> + sb = path->dentry->d_sb;
> + p->f_fstype = sb->s_magic;
> + p->f_dev_major = MAJOR(sb->s_dev);
> + p->f_dev_minor = MINOR(sb->s_dev);
> +
> + memcpy(&p->f_fsid, &buf.f_fsid, sizeof(p->f_fsid));
> + strlcpy(p->f_fs_name, path->dentry->d_sb->s_type->name,
> + sizeof(p->f_fs_name));

Truncation is acceptable or impossible I assume?

> + return sizeof(*p);
> +}
> +
> +static int fsinfo_generic_limits(struct path *path, struct fsinfo_limits *lim)
> +{
> + struct super_block *sb = path->dentry->d_sb;
> +
> + lim->max_file_size.hi = 0;
> + lim->max_file_size.lo = sb->s_maxbytes;
> + lim->max_hard_links = sb->s_max_links;
> + lim->max_uid = UINT_MAX;
> + lim->max_gid = UINT_MAX;
> + lim->max_projid = UINT_MAX;
> + lim->max_filename_len = NAME_MAX;
> + lim->max_symlink_len = PAGE_SIZE;
> + lim->max_xattr_name_len = XATTR_NAME_MAX;
> + lim->max_xattr_body_len = XATTR_SIZE_MAX;
> + lim->max_dev_major = 0xffffff;
> + lim->max_dev_minor = 0xff;
> + return sizeof(*lim);
> +}
> +
> +static int fsinfo_generic_supports(struct path *path, struct fsinfo_supports *c)
> +{
> + struct super_block *sb = path->dentry->d_sb;
> +
> + c->stx_mask = STATX_BASIC_STATS;
> + if (sb->s_d_op && sb->s_d_op->d_automount)
> + c->stx_attributes |= STATX_ATTR_AUTOMOUNT;
> + return sizeof(*c);
> +}
> +
> +static int fsinfo_generic_capabilities(struct path *path,
> + struct fsinfo_capabilities *c)
> +{
> + struct super_block *sb = path->dentry->d_sb;
> +
> + if (sb->s_mtd)
> + fsinfo_set_cap(c, FSINFO_CAP_IS_FLASH_FS);
> + else if (sb->s_bdev)
> + fsinfo_set_cap(c, FSINFO_CAP_IS_BLOCK_FS);
> +
> + if (sb->s_quota_types & QTYPE_MASK_USR)
> + fsinfo_set_cap(c, FSINFO_CAP_USER_QUOTAS);
> + if (sb->s_quota_types & QTYPE_MASK_GRP)
> + fsinfo_set_cap(c, FSINFO_CAP_GROUP_QUOTAS);
> + if (sb->s_quota_types & QTYPE_MASK_PRJ)
> + fsinfo_set_cap(c, FSINFO_CAP_PROJECT_QUOTAS);
> + if (sb->s_d_op && sb->s_d_op->d_automount)
> + fsinfo_set_cap(c, FSINFO_CAP_AUTOMOUNTS);
> + if (sb->s_id[0])
> + fsinfo_set_cap(c, FSINFO_CAP_VOLUME_ID);
> +
> + fsinfo_set_cap(c, FSINFO_CAP_HAS_ATIME);
> + fsinfo_set_cap(c, FSINFO_CAP_HAS_CTIME);
> + fsinfo_set_cap(c, FSINFO_CAP_HAS_MTIME);
> + return sizeof(*c);
> +}
> +
> +static const struct fsinfo_timestamp_info fsinfo_default_timestamp_info = {
> + .atime = {
> + .minimum = S64_MIN,
> + .maximum = S64_MAX,
> + .gran_mantissa = 1,
> + .gran_exponent = 0,
> + },
> + .mtime = {
> + .minimum = S64_MIN,
> + .maximum = S64_MAX,
> + .gran_mantissa = 1,
> + .gran_exponent = 0,
> + },
> + .ctime = {
> + .minimum = S64_MIN,
> + .maximum = S64_MAX,
> + .gran_mantissa = 1,
> + .gran_exponent = 0,
> + },
> + .btime = {
> + .minimum = S64_MIN,
> + .maximum = S64_MAX,
> + .gran_mantissa = 1,
> + .gran_exponent = 0,
> + },
> +};
> +
> +static int fsinfo_generic_timestamp_info(struct path *path,
> + struct fsinfo_timestamp_info *ts)
> +{
> + struct super_block *sb = path->dentry->d_sb;
> + s8 exponent;
> +
> + *ts = fsinfo_default_timestamp_info;
> +
> +
> + if (sb->s_time_gran < 1000000000) {
> + if (sb->s_time_gran < 1000)
> + exponent = -9;
> + else if (sb->s_time_gran < 1000000)
> + exponent = -6;
> + else
> + exponent = -3;
> +
> + ts->atime.gran_exponent = exponent;
> + ts->mtime.gran_exponent = exponent;
> + ts->ctime.gran_exponent = exponent;
> + ts->btime.gran_exponent = exponent;
> + }
> +
> + return sizeof(*ts);
> +}
> +
> +static int fsinfo_generic_volume_uuid(struct path *path,
> + struct fsinfo_volume_uuid *vu)
> +{
> + struct super_block *sb = path->dentry->d_sb;
> +
> + memcpy(vu, &sb->s_uuid, sizeof(*vu));
> + return sizeof(*vu);
> +}
> +
> +static int fsinfo_generic_volume_id(struct path *path, char *buf)
> +{
> + struct super_block *sb = path->dentry->d_sb;
> + size_t len = strlen(sb->s_id);
> +
> + memcpy(buf, sb->s_id, len + 1);
> + return len;
> +}
> +
> +static int fsinfo_generic_name_encoding(struct path *path, char *buf)
> +{
> + static const char encoding[] = "utf8";
> +
> + memcpy(buf, encoding, sizeof(encoding) - 1);
> + return sizeof(encoding) - 1;
> +}
> +
> +/*
> + * Implement some queries generically from stuff in the superblock.
> + */
> +int generic_fsinfo(struct path *path, struct fsinfo_kparams *params)
> +{
> +#define _gen(X, Y) FSINFO_ATTR_##X: return fsinfo_generic_##Y(path, params->buffer)

I'm really not sure that this helps readability in the switch below... :)

> +
> + switch (params->request) {
> + case _gen(STATFS, statfs);
> + case _gen(IDS, ids);
> + case _gen(LIMITS, limits);
> + case _gen(SUPPORTS, supports);
> + case _gen(CAPABILITIES, capabilities);
> + case _gen(TIMESTAMP_INFO, timestamp_info);
> + case _gen(VOLUME_UUID, volume_uuid);
> + case _gen(VOLUME_ID, volume_id);
> + case _gen(NAME_ENCODING, name_encoding);
> + default:
> + return -EOPNOTSUPP;
> + }
> +}
> +EXPORT_SYMBOL(generic_fsinfo);
> +
> +/*
> + * Retrieve the filesystem info. We make some stuff up if the operation is not
> + * supported.
> + */
> +static int vfs_fsinfo(struct path *path, struct fsinfo_kparams *params)
> +{
> + struct dentry *dentry = path->dentry;
> + int (*fsinfo)(struct path *, struct fsinfo_kparams *);
> + int ret;
> +
> + if (params->request == FSINFO_ATTR_FSINFO) {
> + struct fsinfo_fsinfo *info = params->buffer;
> +
> + info->max_attr = FSINFO_ATTR__NR;
> + info->max_cap = FSINFO_CAP__NR;
> + return sizeof(*info);
> + }
> +
> + fsinfo = dentry->d_sb->s_op->fsinfo;
> + if (!fsinfo) {
> + if (!dentry->d_sb->s_op->statfs)
> + return -EOPNOTSUPP;
> + fsinfo = generic_fsinfo;
> + }
> +
> + ret = security_sb_statfs(dentry);
> + if (ret)
> + return ret;
> +
> + if (!params->overlarge)
> + return fsinfo(path, params);
> +
> + while (!signal_pending(current)) {
> + params->usage = 0;
> + ret = fsinfo(path, params);
> + if (ret <= (int)params->buf_size)

He, and this is where the return value discrepancy hits again. Just
doesn't look nice tbh. :)

> + return ret; /* Error or it fitted */
> + kvfree(params->buffer);

That means callers should always memset fsinfo_kparams or this is an
invalid free...

> + params->buffer = NULL;
> + params->buf_size = roundup(ret, PAGE_SIZE);
> + if (params->buf_size > INT_MAX)
> + return -ETOOSMALL;
> + params->buffer = kvmalloc(params->buf_size, GFP_KERNEL);
> + if (!params->buffer)
> + return -ENOMEM;
> + }
> +
> + return -ERESTARTSYS;
> +}
> +
> +static int vfs_fsinfo_path(int dfd, const char __user *filename,
> + struct fsinfo_kparams *params)
> +{
> + struct path path;
> + unsigned lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
> + int ret = -EINVAL;
> +
> + if ((params->at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
> + AT_EMPTY_PATH)) != 0)
> + return -EINVAL;
> +
> + if (params->at_flags & AT_SYMLINK_NOFOLLOW)
> + lookup_flags &= ~LOOKUP_FOLLOW;
> + if (params->at_flags & AT_NO_AUTOMOUNT)
> + lookup_flags &= ~LOOKUP_AUTOMOUNT;
> + if (params->at_flags & AT_EMPTY_PATH)
> + lookup_flags |= LOOKUP_EMPTY;
> +
> +retry:
> + ret = user_path_at(dfd, filename, lookup_flags, &path);
> + if (ret)
> + goto out;
> +
> + ret = vfs_fsinfo(&path, params);
> + path_put(&path);
> + if (retry_estale(ret, lookup_flags)) {
> + lookup_flags |= LOOKUP_REVAL;
> + goto retry;
> + }
> +out:
> + return ret;
> +}
> +
> +static int vfs_fsinfo_fd(unsigned int fd, struct fsinfo_kparams *params)
> +{
> + struct fd f = fdget_raw(fd);
> + int ret = -EBADF;
> +
> + if (f.file) {
> + ret = vfs_fsinfo(&f.file->f_path, params);
> + fdput(f);
> + }
> + return ret;
> +}
> +
> +/*
> + * Return buffer information by requestable attribute.
> + *
> + * STRUCT indicates a fixed-size structure with only one instance.
> + * STRUCT_N indicates a 1D array of STRUCT, indexed by Nth
> + * STRUCT_NM indicates a 2D-array of STRUCT, indexed by Nth, Mth
> + * STRING indicates a string with only one instance.
> + * STRING_N indicates a 1D array of STRING, indexed by Nth
> + * STRING_NM indicates a 2D-array of STRING, indexed by Nth, Mth
> + * OPAQUE indicates a blob that can be larger than 4K.
> + * STRUCT_ARRAY indicates an array of structs that can be larger than 4K

I honestly have a hard time following the documentation here and that
monster table/macro thing below. For example, STRUCT_NM corresponds to
__FSINFO_NM or what? And is this uapi as you're using this in your
samples/test below?

> + *
> + * If an entry is marked STRUCT, STRUCT_N or STRUCT_NM then if no buffer is
> + * supplied to sys_fsinfo(), sys_fsinfo() will handle returning the buffer size
> + * without calling vfs_fsinfo() and the filesystem.
> + *
> + * No struct may have more than 4K bytes.
> + */
> +struct fsinfo_attr_info {
> + u8 type;
> + u8 flags;
> + u16 size;
> +};
> +
> +#define __FSINFO_STRUCT 0
> +#define __FSINFO_STRING 1
> +#define __FSINFO_OPAQUE 2
> +#define __FSINFO_STRUCT_ARRAY 3
> +#define __FSINFO_0 0
> +#define __FSINFO_N 0x0001
> +#define __FSINFO_NM 0x0002
> +
> +#define _Z(T, F, S) { .type = __FSINFO_##T, .flags = __FSINFO_##F, .size = S }
> +#define FSINFO_STRING(X,Y) [FSINFO_ATTR_##X] = _Z(STRING, 0, 0)
> +#define FSINFO_STRUCT(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT, 0, sizeof(struct fsinfo_##Y))
> +#define FSINFO_STRING_N(X,Y) [FSINFO_ATTR_##X] = _Z(STRING, N, 0)
> +#define FSINFO_STRUCT_N(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT, N, sizeof(struct fsinfo_##Y))
> +#define FSINFO_STRING_NM(X,Y) [FSINFO_ATTR_##X] = _Z(STRING, NM, 0)
> +#define FSINFO_STRUCT_NM(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT, NM, sizeof(struct fsinfo_##Y))
> +#define FSINFO_OPAQUE(X,Y) [FSINFO_ATTR_##X] = _Z(OPAQUE, 0, 0)
> +#define FSINFO_STRUCT_ARRAY(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT_ARRAY, 0, sizeof(struct fsinfo_##Y))
> +
> +static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
> + FSINFO_STRUCT (STATFS, statfs),
> + FSINFO_STRUCT (FSINFO, fsinfo),
> + FSINFO_STRUCT (IDS, ids),
> + FSINFO_STRUCT (LIMITS, limits),
> + FSINFO_STRUCT (CAPABILITIES, capabilities),
> + FSINFO_STRUCT (SUPPORTS, supports),
> + FSINFO_STRUCT (TIMESTAMP_INFO, timestamp_info),
> + FSINFO_STRING (VOLUME_ID, volume_id),
> + FSINFO_STRUCT (VOLUME_UUID, volume_uuid),
> + FSINFO_STRING (VOLUME_NAME, -),
> + FSINFO_STRING (NAME_ENCODING, -),
> + FSINFO_STRING (NAME_CODEPAGE, -),
> +};

Can I complain again that this is really annoying to parse.

> +
> +/**
> + * sys_fsinfo - System call to get filesystem information
> + * @dfd: Base directory to pathwalk from or fd referring to filesystem.
> + * @filename: Filesystem to query or NULL.
> + * @_params: Parameters to define request (or NULL for enhanced statfs).
> + * @user_buffer: Result buffer.
> + * @user_buf_size: Size of result buffer.
> + *
> + * Get information on a filesystem. The filesystem attribute to be queried is
> + * indicated by @_params->request, and some of the attributes can have multiple
> + * values, indexed by @_params->Nth and @_params->Mth. If @_params is NULL,
> + * then the 0th fsinfo_attr_statfs attribute is queried. If an attribute does
> + * not exist, EOPNOTSUPP is returned; if the Nth,Mth value does not exist,
> + * ENODATA is returned.
> + *
> + * On success, the size of the attribute's value is returned. If
> + * @user_buf_size is 0 or @user_buffer is NULL, only the size is returned. If
> + * the size of the value is larger than @user_buf_size, it will be truncated by
> + * the copy. If the size of the value is smaller than @user_buf_size then the
> + * excess buffer space will be cleared. The full size of the value will be
> + * returned, irrespective of how much data is actually placed in the buffer.
> + */
> +SYSCALL_DEFINE5(fsinfo,
> + int, dfd, const char __user *, filename,
> + struct fsinfo_params __user *, _params,
> + void __user *, user_buffer, size_t, user_buf_size)
> +{
> + struct fsinfo_attr_info info;
> + struct fsinfo_params user_params;
> + struct fsinfo_kparams params;
> + unsigned int result_size;
> + int ret;
> +
> + memset(&params, 0, sizeof(params));
> +
> + if (_params) {
> + if (copy_from_user(&user_params, _params, sizeof(user_params)))
> + return -EFAULT;
> + if (user_params.__reserved[0] ||
> + user_params.__reserved[1] ||
> + user_params.__reserved[2])
> + return -EINVAL;

Hm, aren't there 6 reserved fields?

> + if (user_params.request >= FSINFO_ATTR__NR)
> + return -EOPNOTSUPP;
> + params.at_flags = user_params.at_flags;
> + params.request = user_params.request;
> + params.Nth = user_params.Nth;
> + params.Mth = user_params.Mth;
> + } else {
> + params.request = FSINFO_ATTR_STATFS;
> + }
> +
> + if (!user_buffer || !user_buf_size) {
> + user_buf_size = 0;
> + user_buffer = NULL;
> + }
> +
> + /* Allocate an appropriately-sized buffer. We will truncate the
> + * contents when we write the contents back to userspace.
> + */
> + info = fsinfo_buffer_info[params.request];
> + if (params.Nth != 0 && !(info.flags & (__FSINFO_N | __FSINFO_NM)))
> + return -ENODATA;
> + if (params.Mth != 0 && !(info.flags & __FSINFO_NM))
> + return -ENODATA;
> +
> + switch (info.type) {
> + case __FSINFO_STRUCT:
> + params.buf_size = info.size;
> + if (user_buf_size == 0)
> + return info.size; /* We know how big the buffer should be */
> + break;
> +
> + case __FSINFO_STRING:
> + params.buf_size = 4096;
> + break;
> +
> + case __FSINFO_OPAQUE:
> + case __FSINFO_STRUCT_ARRAY:
> + /* Opaque blob or array of struct elements. We also create a
> + * buffer that can be used for scratch space.
> + */
> + ret = -ENOMEM;
> + params.scratch_buffer = kmalloc(4096, GFP_KERNEL);
> + if (!params.scratch_buffer)
> + goto error;
> + params.overlarge = true;
> + params.buf_size = 4096;

All the 4096 could probably be macros, FSATTR_GOOD_SIZE or whatever name
you might like.

> + break;
> +
> + default:
> + return -ENOBUFS;
> + }
> +
> + /* We always allocate a buffer for a string, even if buf_size == 0 and
> + * we're not going to return any data. This means that the filesystem
> + * code needn't care about whether the buffer actually exists or not.
> + */
> + ret = -ENOMEM;
> + params.buffer = kvzalloc(params.buf_size, GFP_KERNEL);
> + if (!params.buffer)
> + goto error_scratch;
> +
> + if (filename)
> + ret = vfs_fsinfo_path(dfd, filename, &params);
> + else
> + ret = vfs_fsinfo_fd(dfd, &params);
> + if (ret < 0)
> + goto error_buffer;
> +
> + result_size = ret;
> + if (result_size > user_buf_size)
> + result_size = user_buf_size;
> +
> + if (result_size > 0 &&
> + copy_to_user(user_buffer, params.buffer, result_size)) {
> + ret = -EFAULT;
> + goto error_buffer;
> + }
> +
> + /* Clear any part of the buffer that we won't fill if we're putting a
> + * struct in there. Strings, opaque objects and arrays are expected to
> + * be variable length.
> + */
> + if (info.type == __FSINFO_STRUCT &&
> + user_buf_size > result_size &&
> + clear_user(user_buffer + result_size, user_buf_size - result_size) != 0) {

For consistency you could error check the clear_user() the same way as
copy_to_user(), i.e.

if (copy_to_user()) and if (clear_user()) and not if (clear_user() != 0)

> + ret = -EFAULT;
> + goto error_buffer;
> + }
> +
> +error_buffer:
> + kvfree(params.buffer);
> +error_scratch:
> + kfree(params.scratch_buffer);
> +error:
> + return ret;
> +}
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 6a38b7124143..71ce3b054c42 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -66,6 +66,8 @@ struct fscrypt_info;
> struct fscrypt_operations;
> struct fs_context;
> struct fs_parameter_description;
> +struct fsinfo_kparams;
> +enum fsinfo_attribute;
>
> extern void __init inode_init(void);
> extern void __init inode_init_early(void);
> @@ -1922,6 +1924,9 @@ struct super_operations {
> int (*thaw_super) (struct super_block *);
> int (*unfreeze_fs) (struct super_block *);
> int (*statfs) (struct dentry *, struct kstatfs *);
> +#ifdef CONFIG_FSINFO
> + int (*fsinfo) (struct path *, struct fsinfo_kparams *);
> +#endif
> int (*remount_fs) (struct super_block *, int *, char *);
> void (*umount_begin) (struct super_block *);
>
> diff --git a/include/linux/fsinfo.h b/include/linux/fsinfo.h
> new file mode 100644
> index 000000000000..e17e4f0bae18
> --- /dev/null
> +++ b/include/linux/fsinfo.h
> @@ -0,0 +1,66 @@
> +/* Filesystem information query
> + *
> + * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.
> + */
That should be an SPDX line I would expect. Otherwise Thomas and Greg
can do another round of conversions right after this patchset. :)

> +
> +#ifndef _LINUX_FSINFO_H
> +#define _LINUX_FSINFO_H
> +
> +#ifdef CONFIG_FSINFO
> +
> +#include <uapi/linux/fsinfo.h>
> +
> +struct fsinfo_kparams {
> + __u32 at_flags; /* AT_SYMLINK_NOFOLLOW and similar */
> + enum fsinfo_attribute request; /* What is being asking for */
> + __u32 Nth; /* Instance of it (some may have multiple) */
> + __u32 Mth; /* Subinstance */
> + bool overlarge; /* T if the buffer may be resized */
> + unsigned int usage; /* Amount of buffer used (overlarge=T) */
> + unsigned int buf_size; /* Size of ->buffer[] */
> + void *buffer; /* Where to place the reply */
> + char *scratch_buffer; /* 4K scratch buffer (overlarge=T) */
> +};
> +
> +extern int generic_fsinfo(struct path *, struct fsinfo_kparams *);
> +
> +static inline void fsinfo_set_cap(struct fsinfo_capabilities *c,
> + enum fsinfo_capability cap)
> +{
> + c->capabilities[cap / 8] |= 1 << (cap % 8);
> +}
> +
> +static inline void fsinfo_clear_cap(struct fsinfo_capabilities *c,
> + enum fsinfo_capability cap)
> +{
> + c->capabilities[cap / 8] &= ~(1 << (cap % 8));
> +}
> +
> +/**
> + * fsinfo_set_unix_caps - Set standard UNIX capabilities.
> + * @c: The capabilities mask to alter
> + */
> +static inline void fsinfo_set_unix_caps(struct fsinfo_capabilities *caps)
> +{
> + fsinfo_set_cap(caps, FSINFO_CAP_UIDS);
> + fsinfo_set_cap(caps, FSINFO_CAP_GIDS);
> + fsinfo_set_cap(caps, FSINFO_CAP_DIRECTORIES);
> + fsinfo_set_cap(caps, FSINFO_CAP_SYMLINKS);
> + fsinfo_set_cap(caps, FSINFO_CAP_HARD_LINKS);
> + fsinfo_set_cap(caps, FSINFO_CAP_DEVICE_FILES);
> + fsinfo_set_cap(caps, FSINFO_CAP_UNIX_SPECIALS);
> + fsinfo_set_cap(caps, FSINFO_CAP_SPARSE);
> + fsinfo_set_cap(caps, FSINFO_CAP_HAS_ATIME);
> + fsinfo_set_cap(caps, FSINFO_CAP_HAS_CTIME);
> + fsinfo_set_cap(caps, FSINFO_CAP_HAS_MTIME);
> +}
> +
> +#endif /* CONFIG_FSINFO */
> +
> +#endif /* _LINUX_FSINFO_H */
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index e2870fe1be5b..217d25b62b4f 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -50,6 +50,7 @@ struct stat64;
> struct statfs;
> struct statfs64;
> struct statx;
> +struct fsinfo_params;
> struct __sysctl_args;
> struct sysinfo;
> struct timespec;
> @@ -997,6 +998,9 @@ asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags)
> asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
> siginfo_t __user *info,
> unsigned int flags);
> +asmlinkage long sys_fsinfo(int dfd, const char __user *path,
> + struct fsinfo_params __user *params,
> + void __user *buffer, size_t buf_size);

Nit: There's a bunch of name inconsistency for the arguments between the
stub and the definition:

SYSCALL_DEFINE5(fsinfo,
int, dfd, const char __user *, filename,
struct fsinfo_params __user *, _params,
void __user *, user_buffer, size_t, user_buf_size)

>
> /*
> * Architecture-specific system calls
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index a87904daf103..50ddf5f25122 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -844,9 +844,11 @@ __SYSCALL(__NR_fsconfig, sys_fsconfig)
> __SYSCALL(__NR_fsmount, sys_fsmount)
> #define __NR_fspick 433
> __SYSCALL(__NR_fspick, sys_fspick)
> +#define __NR_fsinfo 434
> +__SYSCALL(__NR_fsinfo, sys_fsinfo)
>
> #undef __NR_syscalls
> -#define __NR_syscalls 434
> +#define __NR_syscalls 435
>
> /*
> * 32 bit systems traditionally used different
> diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
> new file mode 100644
> index 000000000000..a7a7c731d992
> --- /dev/null
> +++ b/include/uapi/linux/fsinfo.h
> @@ -0,0 +1,219 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/* fsinfo() definitions.
> + *
> + * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + */

Do we do SPDX that way? Or isn't this just supposed to be:
// <spdxy stuff>

> +#ifndef _UAPI_LINUX_FSINFO_H
> +#define _UAPI_LINUX_FSINFO_H
> +
> +#include <linux/types.h>
> +#include <linux/socket.h>
> +
> +/*
> + * The filesystem attributes that can be requested. Note that some attributes
> + * may have multiple instances which can be switched in the parameter block.
> + */
> +enum fsinfo_attribute {
> + FSINFO_ATTR_STATFS = 0, /* statfs()-style state */
> + FSINFO_ATTR_FSINFO = 1, /* Information about fsinfo() */
> + FSINFO_ATTR_IDS = 2, /* Filesystem IDs */
> + FSINFO_ATTR_LIMITS = 3, /* Filesystem limits */
> + FSINFO_ATTR_SUPPORTS = 4, /* What's supported in statx, iocflags, ... */
> + FSINFO_ATTR_CAPABILITIES = 5, /* Filesystem capabilities (bits) */
> + FSINFO_ATTR_TIMESTAMP_INFO = 6, /* Inode timestamp info */
> + FSINFO_ATTR_VOLUME_ID = 7, /* Volume ID (string) */
> + FSINFO_ATTR_VOLUME_UUID = 8, /* Volume UUID (LE uuid) */
> + FSINFO_ATTR_VOLUME_NAME = 9, /* Volume name (string) */
> + FSINFO_ATTR_NAME_ENCODING = 10, /* Filename encoding (string) */
> + FSINFO_ATTR_NAME_CODEPAGE = 11, /* Filename codepage (string) */
> + FSINFO_ATTR__NR

Nit/Bikeshed: FSINFO_ATTR_MAX? Seems more intuitive.

> +};
> +
> +/*
> + * Optional fsinfo() parameter structure.
> + *
> + * If this is not given, it is assumed that fsinfo_attr_statfs instance 0,0 is
> + * desired.
> + */
> +struct fsinfo_params {
> + __u32 at_flags; /* AT_SYMLINK_NOFOLLOW and similar flags */
> + __u32 request; /* What is being asking for (enum fsinfo_attribute) */
> + __u32 Nth; /* Instance of it (some may have multiple) */
> + __u32 Mth; /* Subinstance of Nth instance */
> + __u64 __reserved[3]; /* Reserved params; all must be 0 */

Oh, so your commit message uses __reserved[6] and here it's
__reserved[3] and your error check above also only validates
__reserved[3]. Should probably make this consistent. :)

> +};
> +
> +struct fsinfo_u128 {
> +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> + __u64 hi;
> + __u64 lo;
> +#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> + __u64 lo;
> + __u64 hi;
> +#endif
> +};

Hm, I know why you do this custom fsinfo_u128 thingy but for userspace
that is going to be annoying to operate with, e.g. comparing the
size/space of two filesystems etc.

> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_statfs).
> + * - This gives extended filesystem information.
> + */
> +struct fsinfo_statfs {
> + struct fsinfo_u128 f_blocks; /* Total number of blocks in fs */
> + struct fsinfo_u128 f_bfree; /* Total number of free blocks */
> + struct fsinfo_u128 f_bavail; /* Number of free blocks available to ordinary user */
> + struct fsinfo_u128 f_files; /* Total number of file nodes in fs */
> + struct fsinfo_u128 f_ffree; /* Number of free file nodes */
> + struct fsinfo_u128 f_favail; /* Number of file nodes available to ordinary user */
> + __u64 f_bsize; /* Optimal block size */
> + __u64 f_frsize; /* Fragment size */
> + __u64 mnt_attrs; /* Mount attributes (MOUNT_ATTR_*) */
> +};
> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_ids).
> + *
> + * List of basic identifiers as is normally found in statfs().
> + */
> +struct fsinfo_ids {
> + char f_fs_name[15 + 1]; /* Filesystem name */

You should probably make this a macro so userspace can use it in fs-name
length checks too.

> + __u64 f_fsid; /* Short 64-bit Filesystem ID (as statfs) */
> + __u64 f_sb_id; /* Internal superblock ID for sbnotify()/mntnotify() */
> + __u32 f_fstype; /* Filesystem type from linux/magic.h [uncond] */
> + __u32 f_dev_major; /* As st_dev_* from struct statx [uncond] */
> + __u32 f_dev_minor;
> + __u32 __reserved[1];
> +};
> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_limits).
> + *
> + * List of supported filesystem limits.
> + */
> +struct fsinfo_limits {
> + struct fsinfo_u128 max_file_size; /* Maximum file size */
> + struct fsinfo_u128 max_ino; /* Maximum inode number */
> + __u64 max_uid; /* Maximum UID supported */
> + __u64 max_gid; /* Maximum GID supported */
> + __u64 max_projid; /* Maximum project ID supported */
> + __u64 max_hard_links; /* Maximum number of hard links on a file */
> + __u64 max_xattr_body_len; /* Maximum xattr content length */
> + __u32 max_xattr_name_len; /* Maximum xattr name length */
> + __u32 max_filename_len; /* Maximum filename length */
> + __u32 max_symlink_len; /* Maximum symlink content length */
> + __u32 max_dev_major; /* Maximum device major representable */
> + __u32 max_dev_minor; /* Maximum device minor representable */
> + __u32 __reserved[1];
> +};
> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_supports).
> + *
> + * What's supported in various masks, such as statx() attribute and mask bits
> + * and IOC flags.
> + */
> +struct fsinfo_supports {
> + __u64 stx_attributes; /* What statx::stx_attributes are supported */
> + __u32 stx_mask; /* What statx::stx_mask bits are supported */
> + __u32 ioc_flags; /* What FS_IOC_* flags are supported */
> + __u32 win_file_attrs; /* What DOS/Windows FILE_* attributes are supported */
> + __u32 __reserved[1];
> +};
> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_capabilities).
> + *
> + * Bitmask indicating filesystem capabilities where renderable as single bits.
> + */
> +enum fsinfo_capability {
> + FSINFO_CAP_IS_KERNEL_FS = 0, /* fs is kernel-special filesystem */
> + FSINFO_CAP_IS_BLOCK_FS = 1, /* fs is block-based filesystem */
> + FSINFO_CAP_IS_FLASH_FS = 2, /* fs is flash filesystem */
> + FSINFO_CAP_IS_NETWORK_FS = 3, /* fs is network filesystem */
> + FSINFO_CAP_IS_AUTOMOUNTER_FS = 4, /* fs is automounter special filesystem */
> + FSINFO_CAP_IS_MEMORY_FS = 5, /* fs is memory-based filesystem */
> + FSINFO_CAP_AUTOMOUNTS = 6, /* fs supports automounts */
> + FSINFO_CAP_ADV_LOCKS = 7, /* fs supports advisory file locking */
> + FSINFO_CAP_MAND_LOCKS = 8, /* fs supports mandatory file locking */
> + FSINFO_CAP_LEASES = 9, /* fs supports file leases */
> + FSINFO_CAP_UIDS = 10, /* fs supports numeric uids */
> + FSINFO_CAP_GIDS = 11, /* fs supports numeric gids */
> + FSINFO_CAP_PROJIDS = 12, /* fs supports numeric project ids */
> + FSINFO_CAP_STRING_USER_IDS = 13, /* fs supports string user identifiers */
> + FSINFO_CAP_GUID_USER_IDS = 14, /* fs supports GUID user identifiers */
> + FSINFO_CAP_WINDOWS_ATTRS = 15, /* fs has windows attributes */
> + FSINFO_CAP_USER_QUOTAS = 16, /* fs has per-user quotas */
> + FSINFO_CAP_GROUP_QUOTAS = 17, /* fs has per-group quotas */
> + FSINFO_CAP_PROJECT_QUOTAS = 18, /* fs has per-project quotas */
> + FSINFO_CAP_XATTRS = 19, /* fs has xattrs */
> + FSINFO_CAP_JOURNAL = 20, /* fs has a journal */
> + FSINFO_CAP_DATA_IS_JOURNALLED = 21, /* fs is using data journalling */
> + FSINFO_CAP_O_SYNC = 22, /* fs supports O_SYNC */
> + FSINFO_CAP_O_DIRECT = 23, /* fs supports O_DIRECT */
> + FSINFO_CAP_VOLUME_ID = 24, /* fs has a volume ID */
> + FSINFO_CAP_VOLUME_UUID = 25, /* fs has a volume UUID */
> + FSINFO_CAP_VOLUME_NAME = 26, /* fs has a volume name */
> + FSINFO_CAP_VOLUME_FSID = 27, /* fs has a volume FSID */
> + FSINFO_CAP_IVER_ALL_CHANGE = 28, /* i_version represents data + meta changes */
> + FSINFO_CAP_IVER_DATA_CHANGE = 29, /* i_version represents data changes only */
> + FSINFO_CAP_IVER_MONO_INCR = 30, /* i_version incremented monotonically */
> + FSINFO_CAP_DIRECTORIES = 31, /* fs supports (sub)directories */
> + FSINFO_CAP_SYMLINKS = 32, /* fs supports symlinks */
> + FSINFO_CAP_HARD_LINKS = 33, /* fs supports hard links */
> + FSINFO_CAP_HARD_LINKS_1DIR = 34, /* fs supports hard links in same dir only */
> + FSINFO_CAP_DEVICE_FILES = 35, /* fs supports bdev, cdev */
> + FSINFO_CAP_UNIX_SPECIALS = 36, /* fs supports pipe, fifo, socket */
> + FSINFO_CAP_RESOURCE_FORKS = 37, /* fs supports resource forks/streams */
> + FSINFO_CAP_NAME_CASE_INDEP = 38, /* Filename case independence is mandatory */
> + FSINFO_CAP_NAME_NON_UTF8 = 39, /* fs has non-utf8 names */
> + FSINFO_CAP_NAME_HAS_CODEPAGE = 40, /* fs has a filename codepage */
> + FSINFO_CAP_SPARSE = 41, /* fs supports sparse files */
> + FSINFO_CAP_NOT_PERSISTENT = 42, /* fs is not persistent */
> + FSINFO_CAP_NO_UNIX_MODE = 43, /* fs does not support unix mode bits */
> + FSINFO_CAP_HAS_ATIME = 44, /* fs supports access time */
> + FSINFO_CAP_HAS_BTIME = 45, /* fs supports birth/creation time */
> + FSINFO_CAP_HAS_CTIME = 46, /* fs supports change time */
> + FSINFO_CAP_HAS_MTIME = 47, /* fs supports modification time */
> + FSINFO_CAP__NR

Hm, again, maybe better to use FSINFO_CAP_MAX?

> +};
> +
> +struct fsinfo_capabilities {
> + __u8 capabilities[(FSINFO_CAP__NR + 7) / 8];
> +};
> +
> +struct fsinfo_timestamp_one {
> + __s64 minimum; /* Minimum timestamp value in seconds */
> + __u64 maximum; /* Maximum timestamp value in seconds */
> + __u16 gran_mantissa; /* Granularity(secs) = mant * 10^exp */
> + __s8 gran_exponent;
> + __u8 reserved[5];
> +};
> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_timestamp_info).
> + */
> +struct fsinfo_timestamp_info {
> + struct fsinfo_timestamp_one atime; /* Access time */
> + struct fsinfo_timestamp_one mtime; /* Modification time */
> + struct fsinfo_timestamp_one ctime; /* Change time */
> + struct fsinfo_timestamp_one btime; /* Birth/creation time */
> +};
> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_volume_uuid).
> + */
> +struct fsinfo_volume_uuid {
> + __u8 uuid[16];
> +};
> +
> +/*
> + * Information struct for fsinfo(fsinfo_attr_fsinfo).
> + *
> + * This gives information about fsinfo() itself.
> + */
> +struct fsinfo_fsinfo {
> + __u32 max_attr; /* Number of supported attributes (fsinfo_attr__nr) */
> + __u32 max_cap; /* Number of supported capabilities (fsinfo_cap__nr) */
> +};
> +
> +#endif /* _UAPI_LINUX_FSINFO_H */
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 4d9ae5ea6caf..93927072396c 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -51,6 +51,7 @@ COND_SYSCALL_COMPAT(io_pgetevents);
> COND_SYSCALL(io_uring_setup);
> COND_SYSCALL(io_uring_enter);
> COND_SYSCALL(io_uring_register);
> +COND_SYSCALL(fsinfo);
>
> /* fs/xattr.c */
>
> diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
> index a3e4ffd4c773..d3cc8e9a4fd8 100644
> --- a/samples/vfs/Makefile
> +++ b/samples/vfs/Makefile
> @@ -1,10 +1,14 @@
> # List of programs to build
> hostprogs-y := \
> + test-fsinfo \
> test-fsmount \
> test-statx
>
> # Tell kbuild to always build the programs
> always := $(hostprogs-y)
>
> +HOSTCFLAGS_test-fsinfo.o += -I$(objtree)/usr/include
> +HOSTLDLIBS_test-fsinfo += -lm
> +
> HOSTCFLAGS_test-fsmount.o += -I$(objtree)/usr/include
> HOSTCFLAGS_test-statx.o += -I$(objtree)/usr/include
> diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
> new file mode 100644
> index 000000000000..8cce1986df7e
> --- /dev/null
> +++ b/samples/vfs/test-fsinfo.c
> @@ -0,0 +1,551 @@
> +/* Test the fsinfo() system call
> + *
> + * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.
> + */
> +
> +#define _GNU_SOURCE
> +#define _ATFILE_SOURCE
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <stdint.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <ctype.h>
> +#include <errno.h>
> +#include <time.h>
> +#include <math.h>
> +#include <fcntl.h>
> +#include <sys/syscall.h>
> +#include <linux/fsinfo.h>
> +#include <linux/socket.h>
> +#include <sys/stat.h>
> +#include <arpa/inet.h>
> +
> +#ifndef __NR_fsinfo
> +#define __NR_fsinfo -1
> +#endif
> +
> +static bool debug = 0;
> +
> +static __attribute__((unused))
> +ssize_t fsinfo(int dfd, const char *filename, struct fsinfo_params *params,
> + void *buffer, size_t buf_size)
> +{
> + return syscall(__NR_fsinfo, dfd, filename, params, buffer, buf_size);
> +}
> +
> +struct fsinfo_attr_info {
> + unsigned char type;
> + unsigned char flags;
> + unsigned short size;
> +};
> +
> +#define __FSINFO_STRUCT 0
> +#define __FSINFO_STRING 1
> +#define __FSINFO_OVER 2
> +#define __FSINFO_STRUCT_ARRAY 3
> +#define __FSINFO_0 0
> +#define __FSINFO_N 0x0001
> +#define __FSINFO_NM 0x0002
> +
> +#define _Z(T, F, S) { .type = __FSINFO_##T, .flags = __FSINFO_##F, .size = S }
> +#define FSINFO_STRING(X,Y) [FSINFO_ATTR_##X] = _Z(STRING, 0, 0)
> +#define FSINFO_STRUCT(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT, 0, sizeof(struct fsinfo_##Y))
> +#define FSINFO_STRING_N(X,Y) [FSINFO_ATTR_##X] = _Z(STRING, N, 0)
> +#define FSINFO_STRUCT_N(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT, N, sizeof(struct fsinfo_##Y))
> +#define FSINFO_STRING_NM(X,Y) [FSINFO_ATTR_##X] = _Z(STRING, NM, 0)
> +#define FSINFO_STRUCT_NM(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT, NM, sizeof(struct fsinfo_##Y))
> +#define FSINFO_OVERLARGE(X,Y) [FSINFO_ATTR_##X] = _Z(OVER, 0, 0)
> +#define FSINFO_STRUCT_ARRAY(X,Y) [FSINFO_ATTR_##X] = _Z(STRUCT_ARRAY, 0, sizeof(struct fsinfo_##Y))
> +
> +static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
> + FSINFO_STRUCT (STATFS, statfs),
> + FSINFO_STRUCT (FSINFO, fsinfo),
> + FSINFO_STRUCT (IDS, ids),
> + FSINFO_STRUCT (LIMITS, limits),
> + FSINFO_STRUCT (CAPABILITIES, capabilities),
> + FSINFO_STRUCT (SUPPORTS, supports),
> + FSINFO_STRUCT (TIMESTAMP_INFO, timestamp_info),
> + FSINFO_STRING (VOLUME_ID, volume_id),
> + FSINFO_STRUCT (VOLUME_UUID, volume_uuid),
> + FSINFO_STRING (VOLUME_NAME, volume_name),
> + FSINFO_STRING (NAME_ENCODING, name_encoding),
> + FSINFO_STRING (NAME_CODEPAGE, name_codepage),
> +};
> +
> +#define FSINFO_NAME(X,Y) [FSINFO_ATTR_##X] = #Y
> +static const char *fsinfo_attr_names[FSINFO_ATTR__NR] = {
> + FSINFO_NAME (STATFS, statfs),
> + FSINFO_NAME (FSINFO, fsinfo),
> + FSINFO_NAME (IDS, ids),
> + FSINFO_NAME (LIMITS, limits),
> + FSINFO_NAME (CAPABILITIES, capabilities),
> + FSINFO_NAME (SUPPORTS, supports),
> + FSINFO_NAME (TIMESTAMP_INFO, timestamp_info),
> + FSINFO_NAME (VOLUME_ID, volume_id),
> + FSINFO_NAME (VOLUME_UUID, volume_uuid),
> + FSINFO_NAME (VOLUME_NAME, volume_name),
> + FSINFO_NAME (NAME_ENCODING, name_encoding),
> + FSINFO_NAME (NAME_CODEPAGE, name_codepage),
> +};
> +
> +union reply {
> + char buffer[4096];
> + struct fsinfo_statfs statfs;
> + struct fsinfo_fsinfo fsinfo;
> + struct fsinfo_ids ids;
> + struct fsinfo_limits limits;
> + struct fsinfo_supports supports;
> + struct fsinfo_capabilities caps;
> + struct fsinfo_timestamp_info timestamps;
> + struct fsinfo_volume_uuid uuid;
> +};
> +
> +static void dump_hex(unsigned int *data, int from, int to)
> +{
> + unsigned offset, print_offset = 1, col = 0;
> +
> + from /= 4;
> + to = (to + 3) / 4;
> +
> + for (offset = from; offset < to; offset++) {
> + if (print_offset) {
> + printf("%04x: ", offset * 8);
> + print_offset = 0;
> + }
> + printf("%08x", data[offset]);
> + col++;
> + if ((col & 3) == 0) {
> + printf("\n");
> + print_offset = 1;
> + } else {
> + printf(" ");
> + }
> + }
> +
> + if (!print_offset)
> + printf("\n");
> +}
> +
> +static void dump_attr_STATFS(union reply *r, int size)
> +{
> + struct fsinfo_statfs *f = &r->statfs;
> +
> + printf("\n");
> + printf("\tblocks: n=%llu fr=%llu av=%llu\n",
> + (unsigned long long)f->f_blocks.lo,
> + (unsigned long long)f->f_bfree.lo,
> + (unsigned long long)f->f_bavail.lo);
> +
> + printf("\tfiles : n=%llu fr=%llu av=%llu\n",
> + (unsigned long long)f->f_files.lo,
> + (unsigned long long)f->f_ffree.lo,
> + (unsigned long long)f->f_favail.lo);
> + printf("\tbsize : %llu\n", f->f_bsize);
> + printf("\tfrsize: %llu\n", f->f_frsize);
> + printf("\tmntfl : %llx\n", (unsigned long long)f->mnt_attrs);
> +}
> +
> +static void dump_attr_FSINFO(union reply *r, int size)
> +{
> + struct fsinfo_fsinfo *f = &r->fsinfo;
> +
> + printf("max_attr=%u max_cap=%u\n", f->max_attr, f->max_cap);
> +}
> +
> +static void dump_attr_IDS(union reply *r, int size)
> +{
> + struct fsinfo_ids *f = &r->ids;
> +
> + printf("\n");
> + printf("\tdev : %02x:%02x\n", f->f_dev_major, f->f_dev_minor);
> + printf("\tfs : type=%x name=%s\n", f->f_fstype, f->f_fs_name);
> + printf("\tfsid : %llx\n", (unsigned long long)f->f_fsid);
> +}
> +
> +static void dump_attr_LIMITS(union reply *r, int size)
> +{
> + struct fsinfo_limits *f = &r->limits;
> +
> + printf("\n");
> + printf("\tmax file size: %llx%016llx\n",
> + (unsigned long long)f->max_file_size.hi,
> + (unsigned long long)f->max_file_size.lo);
> + printf("\tmax ino: %llx%016llx\n",
> + (unsigned long long)f->max_ino.hi,
> + (unsigned long long)f->max_ino.lo);
> + printf("\tmax ids : u=%llx g=%llx p=%llx\n",
> + (unsigned long long)f->max_uid,
> + (unsigned long long)f->max_gid,
> + (unsigned long long)f->max_projid);
> + printf("\tmax dev : maj=%x min=%x\n",
> + f->max_dev_major, f->max_dev_minor);
> + printf("\tmax links : %llx\n",
> + (unsigned long long)f->max_hard_links);
> + printf("\tmax xattr : n=%x b=%llx\n",
> + f->max_xattr_name_len,
> + (unsigned long long)f->max_xattr_body_len);
> + printf("\tmax len : file=%x sym=%x\n",
> + f->max_filename_len, f->max_symlink_len);
> +}
> +
> +static void dump_attr_SUPPORTS(union reply *r, int size)
> +{
> + struct fsinfo_supports *f = &r->supports;
> +
> + printf("\n");
> + printf("\tstx_attr=%llx\n", (unsigned long long)f->stx_attributes);
> + printf("\tstx_mask=%x\n", f->stx_mask);
> + printf("\tioc_flags=%x\n", f->ioc_flags);
> + printf("\twin_fattrs=%x\n", f->win_file_attrs);
> +}
> +
> +#define FSINFO_CAP_NAME(C) [FSINFO_CAP_##C] = #C
> +static const char *fsinfo_cap_names[FSINFO_CAP__NR] = {
> + FSINFO_CAP_NAME(IS_KERNEL_FS),
> + FSINFO_CAP_NAME(IS_BLOCK_FS),
> + FSINFO_CAP_NAME(IS_FLASH_FS),
> + FSINFO_CAP_NAME(IS_NETWORK_FS),
> + FSINFO_CAP_NAME(IS_AUTOMOUNTER_FS),
> + FSINFO_CAP_NAME(IS_MEMORY_FS),
> + FSINFO_CAP_NAME(AUTOMOUNTS),
> + FSINFO_CAP_NAME(ADV_LOCKS),
> + FSINFO_CAP_NAME(MAND_LOCKS),
> + FSINFO_CAP_NAME(LEASES),
> + FSINFO_CAP_NAME(UIDS),
> + FSINFO_CAP_NAME(GIDS),
> + FSINFO_CAP_NAME(PROJIDS),
> + FSINFO_CAP_NAME(STRING_USER_IDS),
> + FSINFO_CAP_NAME(GUID_USER_IDS),
> + FSINFO_CAP_NAME(WINDOWS_ATTRS),
> + FSINFO_CAP_NAME(USER_QUOTAS),
> + FSINFO_CAP_NAME(GROUP_QUOTAS),
> + FSINFO_CAP_NAME(PROJECT_QUOTAS),
> + FSINFO_CAP_NAME(XATTRS),
> + FSINFO_CAP_NAME(JOURNAL),
> + FSINFO_CAP_NAME(DATA_IS_JOURNALLED),
> + FSINFO_CAP_NAME(O_SYNC),
> + FSINFO_CAP_NAME(O_DIRECT),
> + FSINFO_CAP_NAME(VOLUME_ID),
> + FSINFO_CAP_NAME(VOLUME_UUID),
> + FSINFO_CAP_NAME(VOLUME_NAME),
> + FSINFO_CAP_NAME(VOLUME_FSID),
> + FSINFO_CAP_NAME(IVER_ALL_CHANGE),
> + FSINFO_CAP_NAME(IVER_DATA_CHANGE),
> + FSINFO_CAP_NAME(IVER_MONO_INCR),
> + FSINFO_CAP_NAME(DIRECTORIES),
> + FSINFO_CAP_NAME(SYMLINKS),
> + FSINFO_CAP_NAME(HARD_LINKS),
> + FSINFO_CAP_NAME(HARD_LINKS_1DIR),
> + FSINFO_CAP_NAME(DEVICE_FILES),
> + FSINFO_CAP_NAME(UNIX_SPECIALS),
> + FSINFO_CAP_NAME(RESOURCE_FORKS),
> + FSINFO_CAP_NAME(NAME_CASE_INDEP),
> + FSINFO_CAP_NAME(NAME_NON_UTF8),
> + FSINFO_CAP_NAME(NAME_HAS_CODEPAGE),
> + FSINFO_CAP_NAME(SPARSE),
> + FSINFO_CAP_NAME(NOT_PERSISTENT),
> + FSINFO_CAP_NAME(NO_UNIX_MODE),
> + FSINFO_CAP_NAME(HAS_ATIME),
> + FSINFO_CAP_NAME(HAS_BTIME),
> + FSINFO_CAP_NAME(HAS_CTIME),
> + FSINFO_CAP_NAME(HAS_MTIME),
> +};
> +
> +static void dump_attr_CAPABILITIES(union reply *r, int size)
> +{
> + struct fsinfo_capabilities *f = &r->caps;
> + int i;
> +
> + for (i = 0; i < sizeof(f->capabilities); i++)
> + printf("%02x", f->capabilities[i]);
> + printf("\n");
> + for (i = 0; i < FSINFO_CAP__NR; i++)
> + if (f->capabilities[i / 8] & (1 << (i % 8)))
> + printf("\t- %s\n", fsinfo_cap_names[i]);
> +}
> +
> +static void print_time(struct fsinfo_timestamp_one *t, char stamp)
> +{
> + printf("\t%ctime : gran=%gs range=%llx-%llx\n",
> + stamp,
> + t->gran_mantissa * pow(10., t->gran_exponent),
> + (long long)t->minimum,
> + (long long)t->maximum);
> +}
> +
> +static void dump_attr_TIMESTAMP_INFO(union reply *r, int size)
> +{
> + struct fsinfo_timestamp_info *f = &r->timestamps;
> +
> + printf("\n");
> + print_time(&f->atime, 'a');
> + print_time(&f->mtime, 'm');
> + print_time(&f->ctime, 'c');
> + print_time(&f->btime, 'b');
> +}
> +
> +static void dump_attr_VOLUME_UUID(union reply *r, int size)
> +{
> + struct fsinfo_volume_uuid *f = &r->uuid;
> +
> + printf("%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x"
> + "-%02x%02x%02x%02x%02x%02x\n",
> + f->uuid[ 0], f->uuid[ 1],
> + f->uuid[ 2], f->uuid[ 3],
> + f->uuid[ 4], f->uuid[ 5],
> + f->uuid[ 6], f->uuid[ 7],
> + f->uuid[ 8], f->uuid[ 9],
> + f->uuid[10], f->uuid[11],
> + f->uuid[12], f->uuid[13],
> + f->uuid[14], f->uuid[15]);
> +}
> +
> +/*
> + *
> + */
> +typedef void (*dumper_t)(union reply *r, int size);
> +
> +#define FSINFO_DUMPER(N) [FSINFO_ATTR_##N] = dump_attr_##N
> +static const dumper_t fsinfo_attr_dumper[FSINFO_ATTR__NR] = {
> + FSINFO_DUMPER(STATFS),
> + FSINFO_DUMPER(FSINFO),
> + FSINFO_DUMPER(IDS),
> + FSINFO_DUMPER(LIMITS),
> + FSINFO_DUMPER(SUPPORTS),
> + FSINFO_DUMPER(CAPABILITIES),
> + FSINFO_DUMPER(TIMESTAMP_INFO),
> + FSINFO_DUMPER(VOLUME_UUID),
> +};
> +
> +static void dump_fsinfo(enum fsinfo_attribute attr,
> + struct fsinfo_attr_info about,
> + union reply *r, int size)
> +{
> + dumper_t dumper = fsinfo_attr_dumper[attr];
> + unsigned int len;
> +
> + if (!dumper) {
> + printf("<no dumper>\n");
> + return;
> + }
> +
> + len = about.size;
> + if (about.type == __FSINFO_STRUCT && size < len) {
> + printf("<short data %u/%u>\n", size, len);
> + return;
> + }
> +
> + dumper(r, size);
> +}
> +
> +/*
> + * Try one subinstance of an attribute.
> + */
> +static int try_one(const char *file, struct fsinfo_params *params, bool raw)
> +{
> + struct fsinfo_attr_info about;
> + union reply *r;
> + size_t buf_size = 4096;
> + char *p;
> + int ret;
> +
> + for (;;) {
> + r = malloc(buf_size);
> + if (!r) {
> + perror("malloc");
> + exit(1);
> + }
> + memset(r->buffer, 0xbd, buf_size);
> +
> + errno = 0;
> + ret = fsinfo(AT_FDCWD, file, params, r->buffer, buf_size);
> + if (params->request >= FSINFO_ATTR__NR) {
> + if (ret == -1 && errno == EOPNOTSUPP)
> + exit(0);
> + fprintf(stderr, "Unexpected error for too-large command %u: %m\n",
> + params->request);
> + exit(1);
> + }
> + if (ret == -1)
> + break;
> +
> + if (ret <= buf_size)
> + break;
> + buf_size = (ret + 4096 - 1) & ~(4096 - 1);
> + }
> +
> + if (debug)
> + printf("fsinfo(%s,%s,%u,%u) = %d: %m\n",
> + file, fsinfo_attr_names[params->request],
> + params->Nth, params->Mth, ret);
> +
> + about = fsinfo_buffer_info[params->request];
> + if (ret == -1) {
> + if (errno == ENODATA) {
> + if (!(about.flags & (__FSINFO_N | __FSINFO_NM)) &&
> + params->Nth == 0 && params->Mth == 0) {
> + fprintf(stderr,
> + "Unexpected ENODATA (%u[%u][%u])\n",
> + params->request, params->Nth, params->Mth);
> + exit(1);
> + }
> + return (params->Mth == 0) ? 2 : 1;
> + }
> + if (errno == EOPNOTSUPP) {
> + if (params->Nth > 0 || params->Mth > 0) {
> + fprintf(stderr,
> + "Should return -ENODATA (%u[%u][%u])\n",
> + params->request, params->Nth, params->Mth);
> + exit(1);
> + }
> + //printf("\e[33m%s\e[m: <not supported>\n",
> + // fsinfo_attr_names[attr]);
> + return 2;
> + }
> + perror(file);
> + exit(1);
> + }
> +
> + if (raw) {
> + if (ret > 4096)
> + ret = 4096;
> + dump_hex((unsigned int *)r->buffer, 0, ret);
> + return 0;
> + }
> +
> + switch (about.flags & (__FSINFO_N | __FSINFO_NM)) {
> + case 0:
> + printf("\e[33m%s\e[m: ",
> + fsinfo_attr_names[params->request]);
> + break;
> + case __FSINFO_N:
> + printf("\e[33m%s[%u]\e[m: ",
> + fsinfo_attr_names[params->request],
> + params->Nth);
> + break;
> + case __FSINFO_NM:
> + printf("\e[33m%s[%u][%u]\e[m: ",
> + fsinfo_attr_names[params->request],
> + params->Nth, params->Mth);
> + break;
> + }
> +
> + switch (about.type) {
> + case __FSINFO_STRUCT:
> + dump_fsinfo(params->request, about, r, ret);
> + return 0;
> +
> + case __FSINFO_STRING:
> + if (ret >= 4096) {
> + ret = 4096;
> + r->buffer[4092] = '.';
> + r->buffer[4093] = '.';
> + r->buffer[4094] = '.';
> + r->buffer[4095] = 0;
> + } else {
> + r->buffer[ret] = 0;
> + }
> + for (p = r->buffer; *p; p++) {
> + if (!isprint(*p)) {
> + printf("<non-printable>\n");
> + continue;
> + }
> + }
> + printf("%s\n", r->buffer);
> + return 0;
> +
> + case __FSINFO_OVER:
> + return 0;
> +
> + case __FSINFO_STRUCT_ARRAY:
> + dump_fsinfo(params->request, about, r, ret);
> + return 0;
> +
> + default:
> + fprintf(stderr, "Fishy about %u %u,%u,%u\n",
> + params->request, about.type, about.flags, about.size);
> + exit(1);
> + }
> +}
> +
> +/*
> + *
> + */
> +int main(int argc, char **argv)
> +{
> + struct fsinfo_params params = {
> + .at_flags = AT_SYMLINK_NOFOLLOW,
> + };
> + unsigned int attr;
> + int raw = 0, opt, Nth, Mth;
> +
> + while ((opt = getopt(argc, argv, "adlr"))) {
> + switch (opt) {
> + case 'a':
> + params.at_flags |= AT_NO_AUTOMOUNT;
> + continue;
> + case 'd':
> + debug = true;
> + continue;
> + case 'l':
> + params.at_flags &= ~AT_SYMLINK_NOFOLLOW;
> + continue;
> + case 'r':
> + raw = 1;
> + continue;
> + }
> + break;
> + }
> +
> + argc -= optind;
> + argv += optind;
> +
> + if (argc != 1) {
> + printf("Format: test-fsinfo [-alr] <file>\n");
> + exit(2);
> + }
> +
> + for (attr = 0; attr <= FSINFO_ATTR__NR; attr++) {
> + Nth = 0;
> + do {
> + Mth = 0;
> + do {
> + params.request = attr;
> + params.Nth = Nth;
> + params.Mth = Mth;
> +
> + switch (try_one(argv[0], &params, raw)) {
> + case 0:
> + continue;
> + case 1:
> + goto done_M;
> + case 2:
> + goto done_N;
> + }
> + } while (++Mth < 100);
> +
> + done_M:
> + if (Mth >= 100) {
> + fprintf(stderr, "Fishy: Mth == %u\n", Mth);
> + break;
> + }
> +
> + } while (++Nth < 100);
> +
> + done_N:
> + if (Nth >= 100) {
> + fprintf(stderr, "Fishy: Nth == %u\n", Nth);
> + break;
> + }
> + }
> +
> + return 0;
> +}
>

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