libmount: try absolute target before canonicalize

The path canonicalization is expensive and in many cases unwanted due
to problems with readlink() on unreachable NFS and automounters.

This patch add a possibility to search also by $(CWD)/<path> if the
<path> is relative to reduce number of situation when we convert the
path to the canonical absolute path.

The common use-case:

	# cd /some/long/path
	# umount ./mountpoint

old version:

15543: libmount:      TAB: [0x560a99a54230]: lookup TARGET: './test'
15543: libmount:    CACHE: [0x560a99a54290]: canonicalize path ./test
15543: libmount:    CACHE: [0x560a99a54290]: add entry [ 1] (path): /mnt/test: ./test
15543: libmount:      TAB: [0x560a99a54230]: lookup canonical TARGET: '/mnt/test'
15543: libmount:      CXT: [0x560a99a54050]: umount fs: /mnt/test

new version:

15597: libmount:      TAB: [0xabf230]: lookup TARGET: './test'
15597: libmount:      TAB: [0xabf230]: lookup absolute TARGET: '/mnt/test'
15597: libmount:      CXT: [0xabf050]: umount fs: /mnt/test

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/libmount/src/tab.c b/libmount/src/tab.c
index d7a633cba..a8d835e04 100644
--- a/libmount/src/tab.c
+++ b/libmount/src/tab.c
@@ -867,6 +867,20 @@ struct libmnt_fs *mnt_table_find_target(struct libmnt_table *tb, const char *pat
 		if (mnt_fs_streq_target(fs, path))
 			return fs;
 	}
+
+	/* try absolute path */
+	if (is_relative_path(path) && (cn = absolute_path(path))) {
+		DBG(TAB, ul_debugobj(tb, "lookup absolute TARGET: '%s'", cn));
+		mnt_reset_iter(&itr, direction);
+		while (mnt_table_next_fs(tb, &itr, &fs) == 0) {
+			if (mnt_fs_streq_target(fs, cn)) {
+				free(cn);
+				return fs;
+			}
+		}
+		free(cn);
+	}
+
 	if (!tb->cache || !(cn = mnt_resolve_path(path, tb->cache)))
 		return NULL;