[PATCH 1/3] btrfs-progs: enhance find_option()

[Qu Wenruo <wqu@suse.com>]

There are two minor problems in that function:

- Latest GCC reports dropped 'const' qualifier

  The latest GCC (15.2.1) will report the 'const' qualifier is dropped
  for the strstr() call.

  It looks like the latest GCC has taken the 'const' qualifier checks
  one step further, that any pointer that points into a 'const' pointer
  should also have a 'const' qualifier, to make sure there is no
  modification into the original pointed memory.

  In our case, @options parameter has a 'const' qualifier, thus the
  returned @tmp pointer should also have a 'const' qualifier, or we can
  modify the @options through @tmp.

- No error handling if strdup() failed

Enhance them by:

- Add the 'const' qualifier for @tmp
  This also means we can not use @tmp pointer to modify the newly
  duplicated string.
  Instead use a new @i index to access the new string.

- Return NULL if strdup() failed
  And make the caller check errno for memory allocation failure.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 common/utils.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/common/utils.c b/common/utils.c
index 23dbd9d16781..f183705edb8f 100644
--- a/common/utils.c
+++ b/common/utils.c
@@ -375,19 +375,27 @@ struct mnt_entry {
 /*
  * Find first occurrence of up an option string (as "option=") in @options,
  * separated by comma. Return allocated string as "option=value"
+ *
+ * If NULL is returned, the caller needs to check errno to make sure it's not
+ * caused by memory allocation failure.
  */
 static char *find_option(const char *options, const char *option)
 {
-	char *tmp, *ret;
+	const char *tmp;
+	char *ret;
+	int i;
 
+	errno = 0;
 	tmp = strstr(options, option);
 	if (!tmp)
 		return NULL;
 	ret = strdup(tmp);
-	tmp = ret;
-	while (*tmp && *tmp != ',')
-		tmp++;
-	*tmp = 0;
+	if (!ret)
+		return NULL;
+	i = 0;
+	while (*(ret + i) && *(ret + i) != ',')
+		i++;
+	*(ret + i) = '\0';
 	return ret;
 }
 
@@ -600,6 +608,10 @@ int find_mount_fsroot(const char *subvol, const char *subvolid, char **mount)
 			 * requested by the caller
 			 */
 			opt = find_option(ent.options2, "subvolid=");
+			if (!opt && errno) {
+				ret = -errno;
+				goto out;
+			}
 			if (!opt)
 				goto nextline;
 			value = opt + strlen("subvolid=");
-- 
2.53.0