libmount: mnt_resolve_target: tiptoe around active mount points

Current code in mnt_fs_match_target() and mnt_table_find_target()
already does not canonicalize active mount points (when read from
mountinfo), because they are already canonicalized by the kernel.
Calling realpath(fs->target) on a mount point can hang -- e.g. if the
NFS server is unreachable.

This patch optionally extends this strategy to the general case, that is
when @fs does not directly come from the kernel through mountinfo (for
instance, it may have been parsed from /etc/fstab).

Given @mtab parsed from mountinfo, and if mnt_cache_set_targets(cache,
mtab) is used, then mnt_fs_match_target() and mnt_table_find_target()
check whether @fs->target is a known mount point in the cached
mountinfo, before attempting to canonicalize @fs->target, no matter
where @fs itself comes from. If found in the cached mountinfo,
@fs->target is not canonicalized.

[kzak@redhat.com: - don't allocate libmnt_iter,
                  - add docs for mnt_cache_set_targets(),
                  - fallback to mnt_resolve_path() if no cache->mtab specified,
                  - use streq_except_trailing_slash() to compare paths]

Signed-off-by: Eric Rannaud <e@nanocritical.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/libmount/src/libmount.sym b/libmount/src/libmount.sym
index 088db7749..d827c3101 100644
--- a/libmount/src/libmount.sym
+++ b/libmount/src/libmount.sym
@@ -289,6 +289,8 @@ global:
 } MOUNT_2.23;
 
 MOUNT_2.25 {
+	mnt_cache_set_targets;
+	mnt_resolve_target;
 	mnt_table_uniq_fs;
 	mnt_tag_is_valid;
 } MOUNT_2.24;