Today, xfs_mdrestore from stdin will fail if the -i flag is
specified, because it attempts to rewind the stream after
the initial read of the metablock.  This fails, and
results in an abort with "specified file is not a metadata
dump."

Read the metablock exactly once in main(), validate the magic,
print informational flags if requested, and then pass it to
perform_restore() which will then continue the restore process.

Reported-by: Darrick J. Wong <redacted>
Signed-off-by: Marco A Benatto <redacted>
---
 mdrestore/xfs_mdrestore.c | 55 +++++++++++++++++++++++------------------------
 1 file changed, 27 insertions(+), 28 deletions(-)

diff --git a/mdrestore/xfs_mdrestore.c b/mdrestore/xfs_mdrestore.c
index 0bb4ac8..3db740d 100644
--- a/mdrestore/xfs_mdrestore.c
+++ b/mdrestore/xfs_mdrestore.c

@@ -51,35 +51,34 @@ print_progress(const char *fmt, ...)
        progress_since_warning = 1;
 }

+/*
+ * perform_restore() -- do the actual work to restore the metadump
+ *
+ * @src_f: A FILE pointer to the source metadump
+ * @dst_fd: the file descriptor for the target file
+ * @is_target_file: designates whether the target is a regular file
+ * @mbp: pointer to metadump's first xfs_metablock, read and verified by the caller
+ *
+ * src_f should be positioned just past a read the previously validated metablock
+ */
 static void
 perform_restore(
        FILE                    *src_f,
        int                     dst_fd,
-       int                     is_target_file)
+       int                     is_target_file,
+       const struct xfs_metablock      *mbp)
 {
-       xfs_metablock_t         *metablock;     /* header + index + blocks */
+       struct xfs_metablock    *metablock, tmb;        /* header + index + blocks */
        __be64                  *block_index;
        char                    *block_buffer;
        int                     block_size;
        int                     max_indices;
        int                     cur_index;
        int                     mb_count;
-       xfs_metablock_t         tmb;
        xfs_sb_t                sb;
        int64_t                 bytes_read;

-       /*
-        * read in first blocks (superblock 0), set "inprogress" flag for it,
-        * read in the rest of the file, and if complete, clear SB 0's
-        * "inprogress flag"
-        */
-
-       if (fread(&tmb, sizeof(tmb), 1, src_f) != 1)
-               fatal("error reading from file: %s\n", strerror(errno));
-
-       if (be32_to_cpu(tmb.mb_magic) != XFS_MD_MAGIC)
-               fatal("specified file is not a metadata dump\n");
-
+       tmb = *mbp;
        block_size = 1 << tmb.mb_blocklog;
        max_indices = (block_size - sizeof(xfs_metablock_t)) / sizeof(__be64);

@@ -211,6 +210,7 @@ main(
        int             open_flags;
        struct stat     statbuf;
        int             is_target_file;
+       xfs_metablock_t         mb;

        progname = basename(argv[0]);

@@ -237,7 +237,12 @@ main(
        if (!show_info && argc - optind != 2)
                usage();

-       /* open source */
+       /*
+        * open source and test if this really is a dump. The first metadump block
+        * will be passed to perform_restore() which will continue to read the
+        * file from this point. This avoids rewind the stream, which causes
+        * restore to fail when source was being read from stdin.
+        */
        if (strcmp(argv[optind], "-") == 0) {
                src_f = stdin;
                if (isatty(fileno(stdin)))

@@ -248,15 +253,12 @@ main(
                        fatal("cannot open source dump file\n");
        }

-       if (show_info) {
-               xfs_metablock_t         mb;
-
-               if (fread(&mb, sizeof(mb), 1, src_f) != 1)
-                       fatal("error reading from file: %s\n", strerror(errno));
-
-               if (be32_to_cpu(mb.mb_magic) != XFS_MD_MAGIC)
-                       fatal("specified file is not a metadata dump\n");
+       if (fread(&mb, sizeof(mb), 1, src_f) != 1)
+               fatal("error reading from file: %s\n", strerror(errno));
+       if (mb.mb_magic != cpu_to_be32(XFS_MD_MAGIC))
+               fatal("specified file is not a metadata dump\n");

+       if (show_info) {
                if (mb.mb_info & XFS_METADUMP_INFO_FLAGS) {
                        printf("%s: %sobfuscated, %s log, %s metadata blocks\n",
                        argv[optind],

@@ -270,9 +272,6 @@ main(

                if (argc - optind == 1)
                        exit(0);
-
-               /* Go back to the beginning for the restore function */
-               fseek(src_f, 0L, SEEK_SET);
        }

        optind++;

@@ -301,7 +300,7 @@ main(
        if (dst_fd < 0)
                fatal("couldn't open target \"%s\"\n", argv[optind]);

-       perform_restore(src_f, dst_fd, is_target_file);
+       perform_restore(src_f, dst_fd, is_target_file, &mb);

        close(dst_fd);
        if (src_f != stdin)
--

1.8.3.1