Btrfs: remove all subvol options before mounting top-level

}

/*

 * 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;

}