[PATCH v3 1/3] btrfs-progs: Adapt find_mount_root to verify other fields of mntent struct

[Marcos Paulo de Souza <marcos@mpdesouza.com>]

From: Marcos Paulo de Souza <mpdesouza@suse.com>

Currently find_mount_root searches for all btrfs filesystems
mounted and comparing <path> with mnt_dir of each mountpoint.

But there are cases when we need to find the mountpoint for a determined
subvolid or subvol path, and these informations are present in mnt_opts
of mntent struct.

This patch adds two arguments to find_mount_root (data and flag). The
data argument hold the information that we want to compare, and the flag
argument specifies which field of mntent struct that we want to compare.
Currently there is only one flag, BTRFS_FIND_ROOT_PATH, implementing the
current behavior. The next patch will add a new flag to expand the functionality.

Users of find_mount_root were changed, having the data argument the same
as path, since they are only trying to find the mountpoint based on path alone.

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
---
 cmds/receive.c |  3 ++-
 cmds/send.c    |  6 ++++--
 common/utils.c | 15 ++++++++++++---
 common/utils.h |  8 +++++++-
 4 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/cmds/receive.c b/cmds/receive.c
index 2aaba3ff..dc64480e 100644
--- a/cmds/receive.c
+++ b/cmds/receive.c
@@ -1079,7 +1079,8 @@ static int do_receive(struct btrfs_receive *rctx, const char *tomnt,
 	if (realmnt[0]) {
 		rctx->root_path = realmnt;
 	} else {
-		ret = find_mount_root(dest_dir_full_path, &rctx->root_path);
+		ret = find_mount_root(dest_dir_full_path, dest_dir_full_path,
+				BTRFS_FIND_ROOT_PATH, &rctx->root_path);
 		if (ret < 0) {
 			errno = -ret;
 			error("failed to determine mount point for %s: %m",
diff --git a/cmds/send.c b/cmds/send.c
index b8e3ba12..7757f0da 100644
--- a/cmds/send.c
+++ b/cmds/send.c
@@ -329,7 +329,8 @@ static int init_root_path(struct btrfs_send *sctx, const char *subvol)
 	if (sctx->root_path)
 		goto out;
 
-	ret = find_mount_root(subvol, &sctx->root_path);
+	ret = find_mount_root(subvol, subvol, BTRFS_FIND_ROOT_PATH,
+				&sctx->root_path);
 	if (ret < 0) {
 		errno = -ret;
 		error("failed to determine mount point for %s: %m", subvol);
@@ -659,7 +660,8 @@ static int cmd_send(const struct cmd_struct *cmd, int argc, char **argv)
 			goto out;
 		}
 
-		ret = find_mount_root(subvol, &mount_root);
+		ret = find_mount_root(subvol, subvol, BTRFS_FIND_ROOT_PATH,
+					&mount_root);
 		if (ret < 0) {
 			errno = -ret;
 			error("find_mount_root failed on %s: %m", subvol);
diff --git a/common/utils.c b/common/utils.c
index 1253e87d..1c264455 100644
--- a/common/utils.c
+++ b/common/utils.c
@@ -1248,7 +1248,7 @@ int ask_user(const char *question)
  * return 1 if a mount point is found but not btrfs
  * return <0 if something goes wrong
  */
-int find_mount_root(const char *path, char **mount_root)
+int find_mount_root(const char *path, const char *data, u8 flag, char **mount_root)
 {
 	FILE *mnttab;
 	int fd;
@@ -1258,6 +1258,10 @@ int find_mount_root(const char *path, char **mount_root)
 	int not_btrfs = 1;
 	int longest_matchlen = 0;
 	char *longest_match = NULL;
+	char *cmp_field = NULL;
+	bool found;
+
+	BUG_ON(flag != BTRFS_FIND_ROOT_PATH);
 
 	fd = open(path, O_RDONLY | O_NOATIME);
 	if (fd < 0)
@@ -1269,8 +1273,13 @@ int find_mount_root(const char *path, char **mount_root)
 		return -errno;
 
 	while ((ent = getmntent(mnttab))) {
-		len = strlen(ent->mnt_dir);
-		if (strncmp(ent->mnt_dir, path, len) == 0) {
+		cmp_field = ent->mnt_dir;
+
+		len = strlen(cmp_field);
+
+		found = strncmp(cmp_field, data, len) == 0;
+
+		if (found) {
 			/* match found and use the latest match */
 			if (longest_matchlen <= len) {
 				free(longest_match);
diff --git a/common/utils.h b/common/utils.h
index 119c3881..449e1d3e 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -52,6 +52,11 @@
 #define UNITS_HUMAN			(UNITS_HUMAN_BINARY)
 #define UNITS_DEFAULT			(UNITS_HUMAN)
 
+enum btrfs_find_root_flags {
+	/* check mnt_dir of mntent */
+	BTRFS_FIND_ROOT_PATH = 0
+};
+
 void units_set_mode(unsigned *units, unsigned mode);
 void units_set_base(unsigned *units, unsigned base);
 
@@ -93,7 +98,8 @@ int csum_tree_block(struct btrfs_fs_info *root, struct extent_buffer *buf,
 int ask_user(const char *question);
 int lookup_path_rootid(int fd, u64 *rootid);
 int get_btrfs_mount(const char *dev, char *mp, size_t mp_size);
-int find_mount_root(const char *path, char **mount_root);
+int find_mount_root(const char *path, const char *data, u8 flag,
+		char **mount_root);
 int get_device_info(int fd, u64 devid,
 		struct btrfs_ioctl_dev_info_args *di_args);
 int get_df(int fd, struct btrfs_ioctl_space_args **sargs_ret);
-- 
2.26.2