On Fri, Feb 19, 2021 at 01:08:17PM +0300, Alexey Lyashkov wrote:
> Andreas,
>
> What about to disable a O_DIRECT global on any block devices in the e2fsprogs library as this don’t work on 4k disk drives at all ?
> Instead of fixing an O_DIRECT access with patches sends early.
Why would it not work at all ? This is a fix for a specific problem and
I am not currently aware of ony other problems e2fsprogs should have
with 4k sector size drives. Do you have a specific problem in mind ?
Thanks!
-Lukas
>
>
> Alex
>
> > 19 февр. 2021 г., в 1:20, Andreas Dilger <adilger@xxxxxxxxx> написал(а):
> >
> > On Feb 18, 2021, at 2:51 AM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
> >>
> >> Currently the mmp block is read using O_DIRECT to avoid any caching that
> >> may be done by the VM. However when working with regular files this
> >> creates alignment issues when the device of the host file system has
> >> sector size larger than the blocksize of the file system in the file
> >> we're working with.
> >>
> >> This can be reproduced with t_mmp_fail test when run on the device with
> >> 4k sector size because the mke2fs fails when trying to read the mmp
> >> block.
> >>
> >> Fix it by disabling O_DIRECT when working with regular files. I don't
> >> think there is any risk of doing so since the file system layer, unlike
> >> shared block device, should guarantee cache consistency.
> >>
> >> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> >> Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> >
> > Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> >
> >> ---
> >> v2: Fix comment - it avoids problems when the sector size is larger not
> >> smaller than blocksize
> >>
> >> lib/ext2fs/mmp.c | 22 +++++++++++-----------
> >> 1 file changed, 11 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
> >> index c21ae272..cca2873b 100644
> >> --- a/lib/ext2fs/mmp.c
> >> +++ b/lib/ext2fs/mmp.c
> >> @@ -57,21 +57,21 @@ errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf)
> >> * regardless of how the io_manager is doing reads, to avoid caching of
> >> * the MMP block by the io_manager or the VM. It needs to be fresh. */
> >> if (fs->mmp_fd <= 0) {
> >> + struct stat st;
> >> int flags = O_RDWR | O_DIRECT;
> >>
> >> -retry:
> >> + /*
> >> + * There is no reason for using O_DIRECT if we're working with
> >> + * regular file. Disabling it also avoids problems with
> >> + * alignment when the device of the host file system has sector
> >> + * size larger than blocksize of the fs we're working with.
> >> + */
> >> + if (stat(fs->device_name, &st) == 0 &&
> >> + S_ISREG(st.st_mode))
> >> + flags &= ~O_DIRECT;
> >> +
> >> fs->mmp_fd = open(fs->device_name, flags);
> >> if (fs->mmp_fd < 0) {
> >> - struct stat st;
> >> -
> >> - /* Avoid O_DIRECT for filesystem image files if open
> >> - * fails, since it breaks when running on tmpfs. */
> >> - if (errno == EINVAL && (flags & O_DIRECT) &&
> >> - stat(fs->device_name, &st) == 0 &&
> >> - S_ISREG(st.st_mode)) {
> >> - flags &= ~O_DIRECT;
> >> - goto retry;
> >> - }
> >> retval = EXT2_ET_MMP_OPEN_DIRECT;
> >> goto out;
> >> }
> >> --
> >> 2.26.2
> >>
> >
> >
> > Cheers, Andreas
> >
> >
> >
> >
> >
>
