[PATCH] xfs_copy: fix up initial sb buffer read on CRC fs

[Eric Sandeen <sandeen@xxxxxxxxxxx>]

My prior commit, aaf90a2 xfs_copy: fix copy of hard 4k devices
causes xfs_copy to emit a CRC error warning when copying a
CRC filesystem.

This is because we are now reading the maximum sector size,
and attempting to verify the CRC based on that (likely incorrect)
length.

In xfs_db, we currently just don't verify this read, so it's
not a problem.  In xfs_copy, we almost certainly want to verify.

So, first do the maximal read with no verifier; once it's read,
drop that buffer, and re-read with the proper sector size and
verifier.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---

diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
index 44a32e8..fd96e15 100644
--- a/copy/xfs_copy.c
+++ b/copy/xfs_copy.c
@@ -654,11 +654,17 @@ main(int argc, char **argv)
 
        memset(&mbuf, 0, sizeof(xfs_mount_t));
        libxfs_buftarg_init(&mbuf, xargs.ddev, xargs.logdev, xargs.rtdev);
+       /* We don't yet know the sector size, so read maximal size */
        sbp = libxfs_readbuf(mbuf.m_ddev_targp, XFS_SB_DADDR,
-                            1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT),
-                            0, &xfs_sb_buf_ops);
+                            1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT), 0, NULL);
        sb = &mbuf.m_sb;
        libxfs_sb_from_disk(sb, XFS_BUF_TO_SBP(sbp));
+       /* Do it again, now with proper length and verifier */
+       libxfs_putbuf(sbp);
+       libxfs_purgebuf(sbp);
+       sbp = libxfs_readbuf(mbuf.m_ddev_targp, XFS_SB_DADDR,
+                            1 << (sb->sb_sectlog - BBSHIFT),
+                            0, &xfs_sb_buf_ops);
 
        /*
         * For now, V5 superblock filesystems are not supported without -d;