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SubjectRe: [RFC PATCH 64/68] vfs: Convert devpts to use the new mount API
On Wed, Mar 27, 2019 at 11:48:41PM +0000, David Howells wrote:
> Convert the devpts filesystem to the new internal mount API as the old
> one will be obsoleted and removed. This allows greater flexibility in
> communication of mount parameters between userspace, the VFS and the
> filesystem.
>
> See Documentation/filesystems/mount_api.txt for more information.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: "Eric W. Biederman" <ebiederm@xmission.com>
> cc: Christian Brauner <christian.brauner@ubuntu.com>

One nit below otherwise:

Acked-by: Christian Brauner <christian@brauner.io>

> ---
>
> fs/devpts/inode.c | 265 +++++++++++++++++++++++++----------------------------
> 1 file changed, 124 insertions(+), 141 deletions(-)
>
> diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
> index 553a3f3300ae..ed4a49012570 100644
> --- a/fs/devpts/inode.c
> +++ b/fs/devpts/inode.c
> @@ -15,6 +15,8 @@
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/fs.h>
> +#include <linux/fs_context.h>
> +#include <linux/fs_parser.h>
> #include <linux/sched.h>
> #include <linux/namei.h>
> #include <linux/slab.h>
> @@ -24,7 +26,6 @@
> #include <linux/magic.h>
> #include <linux/idr.h>
> #include <linux/devpts_fs.h>
> -#include <linux/parser.h>
> #include <linux/fsnotify.h>
> #include <linux/seq_file.h>
>
> @@ -109,14 +110,19 @@ enum {
> Opt_err
> };
>
> -static const match_table_t tokens = {
> - {Opt_uid, "uid=%u"},
> - {Opt_gid, "gid=%u"},
> - {Opt_mode, "mode=%o"},
> - {Opt_ptmxmode, "ptmxmode=%o"},
> - {Opt_newinstance, "newinstance"},
> - {Opt_max, "max=%d"},
> - {Opt_err, NULL}
> +static const struct fs_parameter_spec devpts_param_specs[] = {
> + fsparam_u32 ("gid", Opt_gid),
> + fsparam_s32 ("max", Opt_max),
> + fsparam_u32oct ("mode", Opt_mode),
> + fsparam_flag ("newinstance", Opt_newinstance),
> + fsparam_u32oct ("ptmxmode", Opt_ptmxmode),
> + fsparam_u32 ("uid", Opt_uid),
> + {}
> +};
> +
> +static const struct fs_parameter_description devpts_fs_parameters = {
> + .name = "devpts",
> + .specs = devpts_param_specs,
> };
>
> struct pts_fs_info {
> @@ -236,93 +242,56 @@ void devpts_release(struct pts_fs_info *fsi)
> deactivate_super(fsi->sb);
> }
>
> -#define PARSE_MOUNT 0
> -#define PARSE_REMOUNT 1
> -
> /*
> - * parse_mount_options():
> - * Set @opts to mount options specified in @data. If an option is not
> - * specified in @data, set it to its default value.
> - *
> - * Note: @data may be NULL (in which case all options are set to default).
> + * devpts_parse_param - Parse mount parameters
> */
> -static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
> +static int devpts_parse_param(struct fs_context *fc, struct fs_parameter *param)
> {
> - char *p;
> + struct pts_fs_info *fsi = fc->s_fs_info;
> + struct pts_mount_opts *opts = &fsi->mount_opts;
> + struct fs_parse_result result;
> kuid_t uid;
> kgid_t gid;
> -
> - opts->setuid = 0;
> - opts->setgid = 0;
> - opts->uid = GLOBAL_ROOT_UID;
> - opts->gid = GLOBAL_ROOT_GID;
> - opts->mode = DEVPTS_DEFAULT_MODE;
> - opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
> - opts->max = NR_UNIX98_PTY_MAX;
> -
> - /* Only allow instances mounted from the initial mount
> - * namespace to tap the reserve pool of ptys.
> - */
> - if (op == PARSE_MOUNT)
> - opts->reserve =
> - (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
> -
> - while ((p = strsep(&data, ",")) != NULL) {
> - substring_t args[MAX_OPT_ARGS];
> - int token;
> - int option;
> -
> - if (!*p)
> - continue;
> -
> - token = match_token(p, tokens, args);
> - switch (token) {
> - case Opt_uid:
> - if (match_int(&args[0], &option))
> - return -EINVAL;
> - uid = make_kuid(current_user_ns(), option);
> - if (!uid_valid(uid))
> - return -EINVAL;
> - opts->uid = uid;
> - opts->setuid = 1;
> - break;
> - case Opt_gid:
> - if (match_int(&args[0], &option))
> - return -EINVAL;
> - gid = make_kgid(current_user_ns(), option);
> - if (!gid_valid(gid))
> - return -EINVAL;
> - opts->gid = gid;
> - opts->setgid = 1;
> - break;
> - case Opt_mode:
> - if (match_octal(&args[0], &option))
> - return -EINVAL;
> - opts->mode = option & S_IALLUGO;
> - break;
> - case Opt_ptmxmode:
> - if (match_octal(&args[0], &option))
> - return -EINVAL;
> - opts->ptmxmode = option & S_IALLUGO;
> - break;
> - case Opt_newinstance:
> - break;
> - case Opt_max:
> - if (match_int(&args[0], &option) ||
> - option < 0 || option > NR_UNIX98_PTY_MAX)
> - return -EINVAL;
> - opts->max = option;
> - break;
> - default:
> - pr_err("called with bogus options\n");
> - return -EINVAL;
> - }
> + int opt;
> +
> + opt = fs_parse(fc, &devpts_fs_parameters, param, &result);
> + if (opt < 0)
> + return opt;
> +
> + switch (opt) {
> + case Opt_uid:
> + uid = make_kuid(current_user_ns(), result.uint_32);
> + if (!uid_valid(uid))
> + return invalf(fc, "Unknown uid");
> + opts->uid = uid;
> + opts->setuid = 1;
> + break;
> + case Opt_gid:
> + gid = make_kgid(current_user_ns(), result.uint_32);
> + if (!gid_valid(gid))
> + return invalf(fc, "Unknown gid");
> + opts->gid = gid;
> + opts->setgid = 1;
> + break;
> + case Opt_mode:
> + opts->mode = result.uint_32 & S_IALLUGO;
> + break;
> + case Opt_ptmxmode:
> + opts->ptmxmode = result.uint_32 & S_IALLUGO;
> + break;
> + case Opt_newinstance:
> + break;
> + case Opt_max:
> + if (result.uint_32 > NR_UNIX98_PTY_MAX)
> + return invalf(fc, "max out of range");
> + opts->max = result.uint_32;
> + break;
> }
>
> return 0;
> }
>
> -static int mknod_ptmx(struct super_block *sb)
> +static int mknod_ptmx(struct super_block *sb, struct fs_context *fc)
> {
> int mode;
> int rc = -ENOMEM;
> @@ -344,7 +313,7 @@ static int mknod_ptmx(struct super_block *sb)
>
> dentry = d_alloc_name(root, "ptmx");
> if (!dentry) {
> - pr_err("Unable to alloc dentry for ptmx node\n");
> + errorf(fc, "Unable to alloc dentry for ptmx node\n");
> goto out;
> }
>
> @@ -353,7 +322,7 @@ static int mknod_ptmx(struct super_block *sb)
> */
> inode = new_inode(sb);
> if (!inode) {
> - pr_err("Unable to alloc inode for ptmx node\n");
> + errorf(fc, "Unable to alloc inode for ptmx node\n");
> dput(dentry);
> goto out;
> }
> @@ -384,13 +353,23 @@ static void update_ptmx_mode(struct pts_fs_info *fsi)
> }
> }
>
> -static int devpts_remount(struct super_block *sb, int *flags, char *data)
> +static int devpts_reconfigure(struct fs_context *fc)
> {
> - int err;
> - struct pts_fs_info *fsi = DEVPTS_SB(sb);
> - struct pts_mount_opts *opts = &fsi->mount_opts;
> + struct pts_fs_info *fsi = DEVPTS_SB(fc->root->d_sb);
> + struct pts_fs_info *new = fc->s_fs_info;
>
> - err = parse_mount_options(data, PARSE_REMOUNT, opts);
> + /* Apply the revised options. We don't want to change ->reserve.
> + * Ideally, we'd update each option conditionally on it having being

s/being/been/ ?

> + * explicitly changed, but the default is to reset everything so that
> + * would break UAPI...
> + */
> + fsi->mount_opts.setuid = new->mount_opts.setuid;
> + fsi->mount_opts.setgid = new->mount_opts.setgid;
> + fsi->mount_opts.uid = new->mount_opts.uid;
> + fsi->mount_opts.gid = new->mount_opts.gid;
> + fsi->mount_opts.mode = new->mount_opts.mode;
> + fsi->mount_opts.ptmxmode = new->mount_opts.ptmxmode;
> + fsi->mount_opts.max = new->mount_opts.max;
>
> /*
> * parse_mount_options() restores options to default values
> @@ -400,7 +379,7 @@ static int devpts_remount(struct super_block *sb, int *flags, char *data)
> */
> update_ptmx_mode(fsi);
>
> - return err;
> + return 0;
> }
>
> static int devpts_show_options(struct seq_file *seq, struct dentry *root)
> @@ -424,31 +403,13 @@ static int devpts_show_options(struct seq_file *seq, struct dentry *root)
>
> static const struct super_operations devpts_sops = {
> .statfs = simple_statfs,
> - .remount_fs = devpts_remount,
> .show_options = devpts_show_options,
> };
>
> -static void *new_pts_fs_info(struct super_block *sb)
> -{
> - struct pts_fs_info *fsi;
> -
> - fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
> - if (!fsi)
> - return NULL;
> -
> - ida_init(&fsi->allocated_ptys);
> - fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
> - fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
> - fsi->sb = sb;
> -
> - return fsi;
> -}
> -
> -static int
> -devpts_fill_super(struct super_block *s, void *data, int silent)
> +static int devpts_fill_super(struct super_block *s, struct fs_context *fc)
> {
> + struct pts_fs_info *fsi = DEVPTS_SB(s);
> struct inode *inode;
> - int error;
>
> s->s_iflags &= ~SB_I_NODEV;
> s->s_blocksize = 1024;
> @@ -457,20 +418,12 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
> s->s_op = &devpts_sops;
> s->s_d_op = &simple_dentry_operations;
> s->s_time_gran = 1;
> + fsi->sb = s;
>
> - error = -ENOMEM;
> - s->s_fs_info = new_pts_fs_info(s);
> - if (!s->s_fs_info)
> - goto fail;
> -
> - error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
> - if (error)
> - goto fail;
> -
> - error = -ENOMEM;
> inode = new_inode(s);
> if (!inode)
> - goto fail;
> + return -ENOMEM;
> +
> inode->i_ino = 1;
> inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
> inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
> @@ -480,20 +433,11 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
>
> s->s_root = d_make_root(inode);
> if (!s->s_root) {
> - pr_err("get root dentry failed\n");
> - goto fail;
> + errorf(fc, "get root dentry failed");
> + return -ENOMEM;
> }
>
> - error = mknod_ptmx(s);
> - if (error)
> - goto fail_dput;
> -
> - return 0;
> -fail_dput:
> - dput(s->s_root);
> - s->s_root = NULL;
> -fail:
> - return error;
> + return mknod_ptmx(s, fc);
> }
>
> /*
> @@ -502,10 +446,48 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
> * Mount a new (private) instance of devpts. PTYs created in this
> * instance are independent of the PTYs in other devpts instances.
> */
> -static struct dentry *devpts_mount(struct file_system_type *fs_type,
> - int flags, const char *dev_name, void *data)
> +static int devpts_get_tree(struct fs_context *fc)
> +{
> + return vfs_get_super(fc, vfs_get_independent_super, devpts_fill_super);
> +}
> +
> +static void devpts_free_fc(struct fs_context *fc)
> +{
> + kfree(fc->s_fs_info);
> +}
> +
> +static const struct fs_context_operations devpts_context_ops = {
> + .free = devpts_free_fc,
> + .parse_param = devpts_parse_param,
> + .get_tree = devpts_get_tree,
> + .reconfigure = devpts_reconfigure,
> +};
> +
> +/*
> + * Set up the filesystem mount context.
> + */
> +static int devpts_init_fs_context(struct fs_context *fc)
> {
> - return mount_nodev(fs_type, flags, data, devpts_fill_super);
> + struct pts_fs_info *fsi;
> +
> + fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
> + if (!fsi)
> + return -ENOMEM;
> +
> + ida_init(&fsi->allocated_ptys);
> + fsi->mount_opts.uid = GLOBAL_ROOT_UID;
> + fsi->mount_opts.gid = GLOBAL_ROOT_GID;
> + fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
> + fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
> + fsi->mount_opts.max = NR_UNIX98_PTY_MAX;
> +
> + if (fc->purpose == FS_CONTEXT_FOR_MOUNT &&
> + current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns)
> + fsi->mount_opts.reserve = true;
> +
> + fc->s_fs_info = fsi;
> + fc->ops = &devpts_context_ops;
> + return 0;
> }
>
> static void devpts_kill_sb(struct super_block *sb)
> @@ -520,7 +502,8 @@ static void devpts_kill_sb(struct super_block *sb)
>
> static struct file_system_type devpts_fs_type = {
> .name = "devpts",
> - .mount = devpts_mount,
> + .init_fs_context = devpts_init_fs_context,
> + .parameters = &devpts_fs_parameters,
> .kill_sb = devpts_kill_sb,
> .fs_flags = FS_USERNS_MOUNT,
> };
>

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