[PATCH] xfsdump: find root inode, not first inode

[Eric Sandeen <sandeen@redhat.com>]

The prior effort to identify the actual root inode in a filesystem
failed in the (rare) case where inodes were allocated with a lower
number than the root.  As a result, the wrong root inode number
went into the dump, and restore would fail with:

xfsrestore: tree.c:757: tree_begindir: Assertion `ino != persp->p_rootino || hardh == persp->p_rooth' failed.

Fix this by iterating over a chunk's worth of inodes until we find
a directory inode with generation 0, which should only be true
for the real root inode.

Fixes: 25195ebf107 ("xfsdump: handle bind mount targets")
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

diff --git a/dump/content.c b/dump/content.c
index 30232d4..9f9c03b 100644
--- a/dump/content.c
+++ b/dump/content.c
@@ -1384,7 +1384,7 @@ baseuuidbypass:
 	/* figure out the ino for the root directory of the fs
 	 * and get its struct xfs_bstat for inomap_build().  This could
 	 * be a bind mount; don't ask for the mount point inode,
-	 * find the actual lowest inode number in the filesystem.
+	 * actually find the root inode number in the filesystem.
 	 */
 	{
 		stat64_t rootstat;
@@ -1404,20 +1404,36 @@ baseuuidbypass:
 			(struct xfs_bstat *)calloc(1, sizeof(struct xfs_bstat));
 		assert(sc_rootxfsstatp);
 
-		/* Get the first valid (i.e. root) inode in this fs */
-		bulkreq.lastip = (__u64 *)&lastino;
-		bulkreq.icount = 1;
-		bulkreq.ubuffer = sc_rootxfsstatp;
-		bulkreq.ocount = &ocount;
-		if (ioctl(sc_fsfd, XFS_IOC_FSBULKSTAT, &bulkreq) < 0) {
-			mlog(MLOG_ERROR,
-			      _("failed to get bulkstat information for root inode\n"));
+		/*
+		 * Find the root inode in this fs.  It is (rarely) possible to
+		 * have a non-root inode come before the root inode, so iterate
+		 * over a chunk's worth looking for the first dir inode with
+		 * bs_gen == 0, which should only be true for the root inode.
+		 */
+		for (i = 0; i < 64; i++) {
+			bulkreq.lastip = (__u64 *)&lastino;
+			bulkreq.icount = 1;
+			bulkreq.ubuffer = sc_rootxfsstatp;
+			bulkreq.ocount = &ocount;
+			if (ioctl(sc_fsfd, XFS_IOC_FSBULKSTAT, &bulkreq) < 0) {
+				mlog(MLOG_ERROR,
+_("failed to get bulkstat information for root inode\n"));
+				return BOOL_FALSE;
+			}
+			/* found it? */
+			if ((sc_rootxfsstatp->bs_mode & S_IFMT) == S_IFDIR &&
+			    sc_rootxfsstatp->bs_gen == 0)
+				break;
+		}
+
+		if (i == 64) {
+			mlog(MLOG_ERROR, _("failed to find root inode\n"));
 			return BOOL_FALSE;
 		}
 
 		if (sc_rootxfsstatp->bs_ino != rootstat.st_ino)
 			mlog (MLOG_NORMAL | MLOG_NOTE,
-			       _("root ino %lld differs from mount dir ino %lld, bind mount?\n"),
+_("root ino %lld differs from mount dir ino %lld, bind mount?\n"),
 			         sc_rootxfsstatp->bs_ino, rootstat.st_ino);
 	}