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From d80424f5ceaa3a7a8ce7dbf6bacca32f2f05fdeb Mon Sep 17 00:00:00 2001
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From: Lukas Czerner <lczerner@redhat.com>
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Date: Thu, 18 Feb 2021 10:51:46 +0100
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Subject: [PATCH 23/46] mmp: do not use O_DIRECT when working with regular file
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Content-Type: text/plain
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Currently the mmp block is read using O_DIRECT to avoid any caching that
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may be done by the VM. However when working with regular files this
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creates alignment issues when the device of the host file system has
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sector size larger than the blocksize of the file system in the file
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we're working with.
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This can be reproduced with t_mmp_fail test when run on the device with
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4k sector size because the mke2fs fails when trying to read the mmp
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block.
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Fix it by disabling O_DIRECT when working with regular files. I don't
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think there is any risk of doing so since the file system layer, unlike
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shared block device, should guarantee cache consistency.
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Signed-off-by: Lukas Czerner <lczerner@redhat.com>
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Reviewed-by: Eric Sandeen <sandeen@redhat.com>
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Reviewed-by: Andreas Dilger <adilger@dilger.ca>
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Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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---
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lib/ext2fs/mmp.c | 22 +++++++++++-----------
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1 file changed, 11 insertions(+), 11 deletions(-)
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diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
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index eddc66a7..626fe395 100644
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--- a/lib/ext2fs/mmp.c
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+++ b/lib/ext2fs/mmp.c
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@@ -57,21 +57,21 @@ errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf)
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* regardless of how the io_manager is doing reads, to avoid caching of
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* the MMP block by the io_manager or the VM. It needs to be fresh. */
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if (fs->mmp_fd <= 0) {
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+ struct stat st;
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int flags = O_RDWR | O_DIRECT;
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-retry:
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+ /*
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+ * There is no reason for using O_DIRECT if we're working with
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+ * regular file. Disabling it also avoids problems with
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+ * alignment when the device of the host file system has sector
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+ * size larger than blocksize of the fs we're working with.
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+ */
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+ if (stat(fs->device_name, &st) == 0 &&
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+ S_ISREG(st.st_mode))
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+ flags &= ~O_DIRECT;
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+
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fs->mmp_fd = open(fs->device_name, flags);
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if (fs->mmp_fd < 0) {
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- struct stat st;
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-
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- /* Avoid O_DIRECT for filesystem image files if open
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- * fails, since it breaks when running on tmpfs. */
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- if (errno == EINVAL && (flags & O_DIRECT) &&
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- stat(fs->device_name, &st) == 0 &&
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- S_ISREG(st.st_mode)) {
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- flags &= ~O_DIRECT;
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- goto retry;
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- }
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retval = EXT2_ET_MMP_OPEN_DIRECT;
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goto out;
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}
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--
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2.35.1
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