Re: [RFC PATCH 64/68] vfs: Convert devpts to use the new mount API

[Christian Brauner <christian.brauner@canonical.com>]

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,
>  };
>