[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [qemu-xen staging] file-posix: Allow byte-aligned O_DIRECT with NFS
commit 5edc85571e7b7269dce408735eba7507f18ac666 Author: Kevin Wolf <kwolf@xxxxxxxxxx> AuthorDate: Thu Jul 16 16:26:01 2020 +0200 Commit: Kevin Wolf <kwolf@xxxxxxxxxx> CommitDate: Fri Jul 17 14:20:57 2020 +0200 file-posix: Allow byte-aligned O_DIRECT with NFS Since commit a6b257a08e3 ('file-posix: Handle undetectable alignment'), we assume that if we open a file with O_DIRECT and alignment probing returns 1, we just couldn't find out the real alignment requirement because some filesystems make the requirement only for allocated blocks. In this case, a safe default of 4k is used. This is too strict for NFS, which does actually allow byte-aligned requests even with O_DIRECT. Because we can't distinguish both cases with generic code, let's just look at the file system magic and disable s->needs_alignment for NFS. This way, O_DIRECT can still be used on NFS for images that are not aligned to 4k. Signed-off-by: Kevin Wolf <kwolf@xxxxxxxxxx> Reviewed-by: Eric Blake <eblake@xxxxxxxxxx> Message-Id: <20200716142601.111237-3-kwolf@xxxxxxxxxx> Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx> Signed-off-by: Kevin Wolf <kwolf@xxxxxxxxxx> --- block/file-posix.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/block/file-posix.c b/block/file-posix.c index 8067e238cb..ae8190edab 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -62,10 +62,12 @@ #include <sys/ioctl.h> #include <sys/param.h> #include <sys/syscall.h> +#include <sys/vfs.h> #include <linux/cdrom.h> #include <linux/fd.h> #include <linux/fs.h> #include <linux/hdreg.h> +#include <linux/magic.h> #include <scsi/sg.h> #ifdef __s390__ #include <asm/dasd.h> @@ -300,6 +302,28 @@ static int probe_physical_blocksize(int fd, unsigned int *blk_size) #endif } +/* + * Returns true if no alignment restrictions are necessary even for files + * opened with O_DIRECT. + * + * raw_probe_alignment() probes the required alignment and assume that 1 means + * the probing failed, so it falls back to a safe default of 4k. This can be + * avoided if we know that byte alignment is okay for the file. + */ +static bool dio_byte_aligned(int fd) +{ +#ifdef __linux__ + struct statfs buf; + int ret; + + ret = fstatfs(fd, &buf); + if (ret == 0 && buf.f_type == NFS_SUPER_MAGIC) { + return true; + } +#endif + return false; +} + /* Check if read is allowed with given memory buffer and length. * * This function is used to check O_DIRECT memory buffer and request alignment. @@ -629,7 +653,7 @@ static int raw_open_common(BlockDriverState *bs, QDict *options, s->has_discard = true; s->has_write_zeroes = true; - if ((bs->open_flags & BDRV_O_NOCACHE) != 0) { + if ((bs->open_flags & BDRV_O_NOCACHE) != 0 && !dio_byte_aligned(s->fd)) { s->needs_alignment = true; } -- generated by git-patchbot for /home/xen/git/qemu-xen.git#staging
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