libmount: optimize mtab and utab parsing in umount

create 8000 NFS mountpoints:
	#!/bin/bash
	mount=/tmp/mount
	if [ ! -d $mount ]; then
	    mkdir -p $mount
	fi
	for dir in {1..8000}; do
	    if [ ! -d $mount/$dir ]; then
		mkdir -p $mount/$dir
	    fi
	    echo mount $dir
	    mount -t nfs 127.0.0.1:/ $mount/$dir
	done

old version:
	time ./umount /tmp/mount/2255

	real	0m1.254s
	user	0m1.002s
	sys	0m0.238s

new version:
	time ./umount /tmp/mount/2244

	real	0m0.332s
	user	0m0.111s
	sys	0m0.218s

Reported-by: chenditang <chendt.fnst@cn.fujitsu.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/libmount/src/context_umount.c b/libmount/src/context_umount.c
index 17ec1f0a4..566bb2115 100644
--- a/libmount/src/context_umount.c
+++ b/libmount/src/context_umount.c
@@ -38,6 +38,20 @@
 # define UMOUNT_UNUSED    0x80000000	/* Flag guaranteed to be unused */
 #endif
 
+/*
+ * Called by mtab parser to filter out entries, nonzero means that
+ * entry has to be filter out.
+ */
+static int mtab_filter(struct libmnt_fs *fs, void *data)
+{
+	if (!fs || !data)
+		return 0;
+	if (mnt_fs_streq_target(fs, data))
+		return 0;
+	if (mnt_fs_streq_srcpath(fs, data))
+		return 0;
+	return 1;
+}
 
 static int lookup_umount_fs(struct libmnt_context *cxt)
 {
@@ -45,6 +59,8 @@ static int lookup_umount_fs(struct libmnt_context *cxt)
 	const char *tgt;
 	struct libmnt_table *mtab = NULL;
 	struct libmnt_fs *fs;
+	struct libmnt_cache *cache = NULL;
+	char *cn_tgt = NULL;
 
 	assert(cxt);
 	assert(cxt->fs);
@@ -56,7 +72,32 @@ static int lookup_umount_fs(struct libmnt_context *cxt)
 		DBG(CXT, mnt_debug_h(cxt, "umount: undefined target"));
 		return -EINVAL;
 	}
+
+	/*
+	 * The mtab file maybe huge and on systems with utab we have to merge
+	 * userspace mount options into /proc/self/mountinfo. This all is
+	 * expensive. The mtab filter allows to filter out entries, then
+	 * mtab and utab are very tiny files.
+	 *
+	 * *but*... the filter uses mnt_fs_streq_{target,srcpath} functions
+	 * where LABEL, UUID or symlinks are to canonicalized. It means that
+	 * it's usable only for canonicalized stuff (e.g. kernel mountinfo).
+	 */
+	if (!cxt->mtab_writable && *tgt == '/') {
+		/* we'll canonicalized /proc/self/mountinfo */
+		cache = mnt_context_get_cache(cxt);
+		cn_tgt = mnt_resolve_path(tgt, cache);
+		if (cn_tgt)
+			mnt_context_set_tabfilter(cxt, mtab_filter, cn_tgt);
+	}
 	rc = mnt_context_get_mtab(cxt, &mtab);
+
+	if (cn_tgt) {
+		mnt_context_set_tabfilter(cxt, NULL, NULL);
+		if (!cache)
+			free(cn_tgt);
+	}
+
 	if (rc) {
 		DBG(CXT, mnt_debug_h(cxt, "umount: failed to read mtab"));
 		return rc;