[PATCH 12/25] xfs_copy: use uncached buffer reads to get the superblock

Darrick J. Wong
2020-02-25T00:12:49Z

Upon startup, xfs_copy needs to read the filesystem superblock to mount
the filesystem. We cannot know the filesystem sector size until we read
the superblock, but we also do not want to introduce aliasing in the
buffer cache. Convert this code to the new uncached buffer read API so
that we can stop open-coding it.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
copy/xfs_copy.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
index 9e9719a0..5cab1a5f 100644
--- a/copy/xfs_copy.c
+++ b/copy/xfs_copy.c
@@ -562,6 +562,7 @@ main(int argc, char **argv)
libxfs_init_t xargs;
thread_args *tcarg;
struct stat statbuf;
+ int error;

progname = basename(argv[0]);

@@ -710,14 +711,20 @@ main(int argc, char **argv)

/* We don't yet know the sector size, so read maximal size */
libxfs_buftarg_init(&mbuf, xargs.ddev, xargs.logdev, xargs.rtdev);
- sbp = libxfs_buf_read(mbuf.m_ddev_targp, XFS_SB_DADDR,
- 1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT), 0, NULL);
+ error = -libxfs_buf_read_uncached(mbuf.m_ddev_targp, XFS_SB_DADDR,
+ 1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT), 0, &sbp, NULL);
+ if (error) {
+ do_log(_("%s: couldn't read superblock, error=%d\n"),
+ progname, error);
+ exit(1);
+ }
+
sb = &mbuf.m_sb;
libxfs_sb_from_disk(sb, XFS_BUF_TO_SBP(sbp));

/* Do it again, now with proper length and verifier */
libxfs_buf_relse(sbp);
- libxfs_purgebuf(sbp);
+
sbp = libxfs_buf_read(mbuf.m_ddev_targp, XFS_SB_DADDR,
1 << (sb->sb_sectlog - BBSHIFT),
0, &xfs_sb_buf_ops);