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SubjectRe: [PATCH 03/25] vfs: Allow fsinfo() to query what's in an fs_context [ver #14]
On Mon, Jun 24, 2019 at 03:09:14PM +0100, David Howells wrote:
> Allow fsinfo() to be used to query the filesystem attached to an fs_context
> once a superblock has been created or if it comes from fspick().
>
> The caller must specify AT_FSINFO_FROM_FSOPEN in the parameters and must

Yeah, I like that better than how it was before.

> supply the fd from fsopen() as dfd and must set filename to NULL.
>
> This is done with something like:
>
> fd = fsopen("ext4", 0);
> ...
> struct fsinfo_params params = {
> .at_flags = AT_FSINFO_FROM_FSOPEN;
> ...
> };
> fsinfo(fd, NULL, &params, ...);
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
>
> fs/fsinfo.c | 46 +++++++++++++++++++++++++++++++++++++++++++-
> fs/statfs.c | 2 +-
> include/uapi/linux/fcntl.h | 2 ++
> 3 files changed, 48 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fsinfo.c b/fs/fsinfo.c
> index 49b46f96dda3..c24701f994d1 100644
> --- a/fs/fsinfo.c
> +++ b/fs/fsinfo.c
> @@ -8,6 +8,7 @@
> #include <linux/security.h>
> #include <linux/uaccess.h>
> #include <linux/fsinfo.h>
> +#include <linux/fs_context.h>
> #include <uapi/linux/mount.h>
> #include "internal.h"
>
> @@ -340,6 +341,42 @@ static int vfs_fsinfo_fd(unsigned int fd, struct fsinfo_kparams *params)
> return ret;
> }
>
> +/*
> + * Allow access to an fs_context object as created by fsopen() or fspick().
> + */
> +static int vfs_fsinfo_fscontext(int fd, struct fsinfo_kparams *params)
> +{
> + struct fs_context *fc;
> + struct fd f = fdget(fd);
> + int ret;
> +
> + if (!f.file)
> + return -EBADF;
> +
> + ret = -EINVAL;
> + if (f.file->f_op == &fscontext_fops)

Don't you mean != ?

if (f.file->f_op != &fscontext_fops)

> + goto out_f;
> + ret = -EOPNOTSUPP;
> + if (fc->ops == &legacy_fs_context_ops)
> + goto out_f;
> +
> + ret = mutex_lock_interruptible(&fc->uapi_mutex);
> + if (ret == 0) {
> + ret = -EIO;

Why EIO when there's no root dentry?

> + if (fc->root) {
> + struct path path = { .dentry = fc->root };
> +
> + ret = vfs_fsinfo(&path, params);
> + }
> +
> + mutex_unlock(&fc->uapi_mutex);
> + }
> +
> +out_f:
> + fdput(f);
> + return ret;
> +}
> +
> /*
> * Return buffer information by requestable attribute.
> *
> @@ -445,6 +482,9 @@ SYSCALL_DEFINE5(fsinfo,
> params.request = user_params.request;
> params.Nth = user_params.Nth;
> params.Mth = user_params.Mth;
> +

[1]:

> + if ((params.at_flags & AT_FSINFO_FROM_FSOPEN) && filename)
> + return -EINVAL;
> } else {
> params.request = FSINFO_ATTR_STATFS;
> }
> @@ -453,6 +493,8 @@ SYSCALL_DEFINE5(fsinfo,
> user_buf_size = 0;
> user_buffer = NULL;
> }
> + if ((params.at_flags & AT_FSINFO_FROM_FSOPEN) && filename)
> + return -EINVAL;

Sorry, why is this checked twice (see [1])? Or is the diff just
misleading here?

>
> /* Allocate an appropriately-sized buffer. We will truncate the
> * contents when we write the contents back to userspace.
> @@ -500,7 +542,9 @@ SYSCALL_DEFINE5(fsinfo,
> if (!params.buffer)
> goto error_scratch;
>
> - if (filename)
> + if (params.at_flags & AT_FSINFO_FROM_FSOPEN)
> + ret = vfs_fsinfo_fscontext(dfd, &params);
> + else if (filename)
> ret = vfs_fsinfo_path(dfd, filename, &params);
> else
> ret = vfs_fsinfo_fd(dfd, &params);
> diff --git a/fs/statfs.c b/fs/statfs.c
> index eea7af6f2f22..b9b63d9f4f24 100644
> --- a/fs/statfs.c
> +++ b/fs/statfs.c
> @@ -86,7 +86,7 @@ int vfs_statfs(const struct path *path, struct kstatfs *buf)
> int error;
>
> error = statfs_by_dentry(path->dentry, buf);
> - if (!error)
> + if (!error && path->mnt)
> buf->f_flags = calculate_f_flags(path->mnt);
> return error;
> }
> diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
> index 1d338357df8a..6a2402a8fa30 100644
> --- a/include/uapi/linux/fcntl.h
> +++ b/include/uapi/linux/fcntl.h
> @@ -91,6 +91,8 @@
> #define AT_STATX_FORCE_SYNC 0x2000 /* - Force the attributes to be sync'd with the server */
> #define AT_STATX_DONT_SYNC 0x4000 /* - Don't sync attributes with the server */
>
> +#define AT_FSINFO_FROM_FSOPEN 0x2000 /* Examine the fs_context attached to dfd by fsopen() */
> +
> #define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
>
>
>

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