commit ed350fc6c49155ec398866ebef1d59be02636bce
Author: Eric Sandeen <sandeen@sandeen.net>
Date:   Wed Jul 16 13:53:47 2014 +1000

    libxcmd: make all comparisons using realpath'd paths
    
    Both mountpoints and devices can be symlinks, so given a path
    to look for, and mountpoints/devices from the system, use
    realpath() on *everything* before making the comparison to see
    if our path is a match.
    
    So, with symlinks for mount points as well as for devices:
    
    # ls -l /dev/mapper/testvg-lvol0
    lrwxrwxrwx. 1 root root 7 Jul 11 19:24 /dev/mapper/testvg-lvol0 -> ../dm-3
    # ls -l /mnt/scratch2
    lrwxrwxrwx. 1 root root 12 Jul 11 19:57 /mnt/scratch2 -> /mnt/scratch
    
    this should all work, and does now:
    
    # xfs_quota -xc "report -h" /mnt/scratch2
    User quota on /mnt/scratch (/dev/mapper/testvg-lvol0)
                            Blocks
    User ID      Used   Soft   Hard Warn/Grace
    ---------- ---------------------------------
    root            0      0      0  00 [------]
    
    # xfs_quota -xc "report -h" /mnt/scratch
    User quota on /mnt/scratch (/dev/mapper/testvg-lvol0)
                            Blocks
    User ID      Used   Soft   Hard Warn/Grace
    ---------- ---------------------------------
    root            0      0      0  00 [------]
    
    # xfs_quota -xc "report -h" /dev/dm-3
    User quota on /mnt/scratch (/dev/mapper/testvg-lvol0)
                            Blocks
    User ID      Used   Soft   Hard Warn/Grace
    ---------- ---------------------------------
    root            0      0      0  00 [------]
    
    # xfs_quota -xc "report -h" /dev/mapper/testvg-lvol0
    User quota on /mnt/scratch (/dev/mapper/testvg-lvol0)
                            Blocks
    User ID      Used   Soft   Hard Warn/Grace
    ---------- ---------------------------------
    root            0      0      0  00 [------]
    
    The commit:
    
    050a7f1 xfsprogs: handle symlinks etc in fs_table_initialise_mounts()
    
    tried to fix this earlier, but only worked one way;
    it compared the argument path in both given and realpath
    form to the paths in getmntent, but did not compare to
    the realpaths of the getmntent devices.
    
    If we reduce everything, everywhere, to a realpath(), we've
    got our best shot at finding the match.
    
    Signed-off-by: Eric Sandeen <sandeen@redhat.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/libxcmd/paths.c b/libxcmd/paths.c
index 7b0e434..443adbb 100644
--- a/libxcmd/paths.c
+++ b/libxcmd/paths.c
@@ -269,6 +269,9 @@ out_nomem:
 /*
  * If *path is NULL, initialize the fs table with all xfs mount points in mtab
  * If *path is specified, search for that path in mtab
+ *
+ * Everything - path, devices, and mountpoints - are boiled down to realpath()
+ * for comparison, but fs_table is populated with what comes from getmntent.
  */
 static int
 fs_table_initialise_mounts(
@@ -278,7 +281,7 @@ fs_table_initialise_mounts(
 	FILE		*mtp;
 	char		*fslog, *fsrt;
 	int		error, found;
-	char		*rpath = NULL;
+	char		rpath[PATH_MAX], rmnt_fsname[PATH_MAX], rmnt_dir[PATH_MAX];
 
 	error = found = 0;
 	fslog = fsrt = NULL;
@@ -294,17 +297,20 @@ fs_table_initialise_mounts(
 
 	/* Use realpath to resolve symlinks, relative paths, etc */
 	if (path)
-		if ((rpath = realpath(path, NULL)) == NULL)
-			return ENOENT;
+		if (!realpath(path, rpath))
+			return errno;
 
 	while ((mnt = getmntent(mtp)) != NULL) {
 		if (strcmp(mnt->mnt_type, "xfs") != 0)
 			continue;
+		if (!realpath(mnt->mnt_dir, rmnt_dir))
+			continue;
+		if (!realpath(mnt->mnt_fsname, rmnt_fsname))
+			continue;
+
 		if (path &&
-		    ((strcmp(path, mnt->mnt_dir) != 0) &&
-		     (strcmp(path, mnt->mnt_fsname) != 0) &&
-		     (strcmp(rpath, mnt->mnt_dir) != 0) &&
-		     (strcmp(rpath, mnt->mnt_fsname) != 0)))
+		    ((strcmp(rpath, rmnt_dir) != 0) &&
+		     (strcmp(rpath, rmnt_fsname) != 0)))
 			continue;
 		if (fs_extract_mount_options(mnt, &fslog, &fsrt))
 			continue;
@@ -316,7 +322,6 @@ fs_table_initialise_mounts(
 		}
 	}
 	endmntent(mtp);
-	free(rpath);
 
 	if (path && !found)
 		error = ENXIO;
@@ -330,6 +335,9 @@ fs_table_initialise_mounts(
 /*
  * If *path is NULL, initialize the fs table with all xfs mount points in mtab
  * If *path is specified, search for that path in mtab
+ *
+ * Everything - path, devices, and mountpoints - are boiled down to realpath()
+ * for comparison, but fs_table is populated with what comes from getmntinfo.
  */
 static int
 fs_table_initialise_mounts(
@@ -337,7 +345,7 @@ fs_table_initialise_mounts(
 {
 	struct statfs	*stats;
 	int		i, count, error, found;
-	char		*rpath = NULL;
+	char		rpath[PATH_MAX], rmntfromname[PATH_MAX], rmntonname[PATH_MAX];
 
 	error = found = 0;
 	if ((count = getmntinfo(&stats, 0)) < 0) {
@@ -348,17 +356,20 @@ fs_table_initialise_mounts(
 
 	/* Use realpath to resolve symlinks, relative paths, etc */
 	if (path)
-		if ((rpath = realpath(path, NULL)) == NULL)
-			return ENOENT;
+		if (!realpath(path, rpath))
+			return errno;
 
 	for (i = 0; i < count; i++) {
 		if (strcmp(stats[i].f_fstypename, "xfs") != 0)
 			continue;
+		if (!realpath(stats[i].f_mntfromname, rmntfromname))
+			continue;
+		if (!realpath(stats[i].f_mntonname, rmnttomname)))
+			continue;
+
 		if (path &&
-		    ((strcmp(path, stats[i].f_mntonname) != 0) &&
-		     (strcmp(path, stats[i].f_mntfromname) != 0) &&
-		     (strcmp(rpath, stats[i].f_mntonname) != 0) &&
-		     (strcmp(rpath, stats[i].f_mntfromname) != 0)))
+		    ((strcmp(rpath, rmntonname) != 0) &&
+		     (strcmp(rpath, rmntfromname) != 0)))
 			continue;
 		/* TODO: external log and realtime device? */
 		(void) fs_table_insert(stats[i].f_mntonname, 0,
@@ -369,7 +380,6 @@ fs_table_initialise_mounts(
 			break;
 		}
 	}
-	free(rpath);
 	if (path && !found)
 		error = ENXIO;