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Commit e6e4dbe8 authored by Omar Sandoval's avatar Omar Sandoval Committed by Chris Mason
Browse files

Btrfs: remove all subvol options before mounting top-level 



Currently, setup_root_args() substitutes 's/subvol=[^,]*/subvolid=0/'.
But, this means that if the user passes both a subvol and subvolid for
some reason, we won't actually mount the top-level when we recursively
mount. For example, consider:

mkfs.btrfs -f /dev/sdb
mount /dev/sdb /mnt
btrfs subvol create /mnt/subvol1 # subvolid=257
btrfs subvol create /mnt/subvol2 # subvolid=258
umount /mnt
mount -osubvol=/subvol1,subvolid=258 /dev/sdb /mnt

In the final mount, subvol=/subvol1,subvolid=258 becomes
subvolid=0,subvolid=258, and the last option takes precedence, so we
mount subvol2 and try to look up subvol1 inside of it, which fails.

So, instead, do a thorough scan through the argument list and remove any
subvol= and subvolid= options, then append subvolid=0 to the end. This
implicitly makes subvol= take precedence over subvolid=, but we're about
to add a stricter check for that. This also makes setup_root_args() more
generic, which we'll need soon.

Reviewed-by: default avatarDavid Sterba <dsterba@suse.cz>
Signed-off-by: default avatarOmar Sandoval <osandov@osandov.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent 773cd04e

fs/btrfs/super.c

+20 −36
Original line number Diff line number Diff line
@@ -1133,52 +1133,36 @@ static inline int is_subvolume_inode(struct inode *inode) 
}



/*

 * This will strip out the subvol=%s argument for an argument string and add

 * subvolid=0 to make sure we get the actual tree root for path walking to the

 * subvol we want.

 * This will add subvolid=0 to the argument string while removing any subvol=

 * and subvolid= arguments to make sure we get the top-level root for path

 * walking to the subvol we want.

 */

static char *setup_root_args(char *args)

{

	unsigned len = strlen(args) + 2 + 1;

	char *src, *dst, *buf;

	char *buf, *dst, *sep;



	/*

	 * We need the same args as before, but with this substitution:

	 * s!subvol=[^,]+!subvolid=0!

	 *

	 * Since the replacement string is up to 2 bytes longer than the

	 * original, allocate strlen(args) + 2 + 1 bytes.

	 */

	if (!args)

		return kstrdup("subvolid=0", GFP_NOFS);



	src = strstr(args, "subvol=");

	/* This shouldn't happen, but just in case.. */

	if (!src)

		return NULL;



	buf = dst = kmalloc(len, GFP_NOFS);

	/* The worst case is that we add ",subvolid=0" to the end. */

	buf = dst = kmalloc(strlen(args) + strlen(",subvolid=0") + 1, GFP_NOFS);

	if (!buf)

		return NULL;



	/*

	 * If the subvol= arg is not at the start of the string,

	 * copy whatever precedes it into buf.

	 */

	if (src != args) {

		*src++ = '\0';

		strcpy(buf, args);

		dst += strlen(args);

	while (1) {

		sep = strchrnul(args, ',');

		if (!strstarts(args, "subvol=") &&

		    !strstarts(args, "subvolid=")) {

			memcpy(dst, args, sep - args);

			dst += sep - args;

			*dst++ = ',';

		}

		if (*sep)

			args = sep + 1;

		else

			break;

	}



	strcpy(dst, "subvolid=0");

	dst += strlen("subvolid=0");



	/*

	 * If there is a "," after the original subvol=... string,

	 * copy that suffix into our buffer.  Otherwise, we're done.

	 */

	src = strchr(src, ',');

	if (src)

		strcpy(dst, src);



	return buf;

}