Re: [PATCH] xfs_mdrestore: Don't rewind source file stream

[Marco Benatto <marco.antonio.780@gmail.com>]

Hi Darrick,

just resent with the changes for the reviews you mentioned.

Please, let me know if this seems ok now.

Thanks,

On Sat, Feb 3, 2018 at 11:16 AM, Marco A Benatto
<marco.antonio.780@gmail.com> wrote:
> 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 <darrick.wong@oracle.com>
> Signed-off-by: Marco A Benatto <marco.antonio.780@gmail.com>
> ---
>  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
>



-- 
Marco Antonio Benatto
Linux user ID: #506236