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nfs: add 'noalignwrite' option for lock-less 'lost writes' prevention

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There are some applications that write to predefined non-overlapping
file offsets from multiple clients and therefore don't need to rely on
file locking. However, if these applications want non-aligned offsets
and sizes they need to either use locks or risk data corruption, as the
NFS client defaults to extending writes to whole pages.

This commit adds a new mount option `noalignwrite`, which allows to turn
that off and avoid the need of locking, as long as these applications
don't overlap on offsets.

Signed-off-by: Dan Aloni <dan.aloni@vastdata.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
This commit is contained in:
Dan Aloni 2024-07-24 14:07:12 +03:00 committed by Anna Schumaker
parent 6d26c5e4d8
commit dfb07e990a
4 changed files with 15 additions and 0 deletions
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8
fs/nfs/fs_context.c
View File

@ -49,6 +49,7 @@ enum nfs_param {
Opt_bsize,
Opt_clientaddr,
Opt_cto,
Opt_alignwrite,
Opt_fg,
Opt_fscache,
Opt_fscache_flag,
@ -149,6 +150,7 @@ static const struct fs_parameter_spec nfs_fs_parameters[] = {
fsparam_u32 ("bsize", Opt_bsize),
fsparam_string("clientaddr", Opt_clientaddr),
fsparam_flag_no("cto", Opt_cto),
fsparam_flag_no("alignwrite", Opt_alignwrite),
fsparam_flag ("fg", Opt_fg),
fsparam_flag_no("fsc", Opt_fscache_flag),
fsparam_string("fsc", Opt_fscache),
@ -592,6 +594,12 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
else
ctx->flags |= NFS_MOUNT_TRUNK_DISCOVERY;
break;
case Opt_alignwrite:
if (result.negated)
ctx->flags |= NFS_MOUNT_NO_ALIGNWRITE;
else
ctx->flags &= ~NFS_MOUNT_NO_ALIGNWRITE;
break;
case Opt_ac:
if (result.negated)
ctx->flags |= NFS_MOUNT_NOAC;

3
fs/nfs/super.c
View File

@ -551,6 +551,9 @@ static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss,
else
seq_puts(m, ",local_lock=posix");
if (nfss->flags & NFS_MOUNT_NO_ALIGNWRITE)
seq_puts(m, ",noalignwrite");
if (nfss->flags & NFS_MOUNT_WRITE_EAGER) {
if (nfss->flags & NFS_MOUNT_WRITE_WAIT)
seq_puts(m, ",write=wait");

3
fs/nfs/write.c
View File

@ -1295,7 +1295,10 @@ static int nfs_can_extend_write(struct file *file, struct folio *folio,
struct file_lock_context *flctx = locks_inode_context(inode);
struct file_lock *fl;
int ret;
unsigned int mntflags = NFS_SERVER(inode)->flags;
if (mntflags & NFS_MOUNT_NO_ALIGNWRITE)
return 0;
if (file->f_flags & O_DSYNC)
return 0;
if (!nfs_folio_write_uptodate(folio, pagelen))

1
include/linux/nfs_fs_sb.h
View File

@ -158,6 +158,7 @@ struct nfs_server {
#define NFS_MOUNT_WRITE_WAIT 0x02000000
#define NFS_MOUNT_TRUNK_DISCOVERY 0x04000000
#define NFS_MOUNT_SHUTDOWN 0x08000000
#define NFS_MOUNT_NO_ALIGNWRITE 0x10000000
unsigned int fattr_valid; /* Valid attributes */
unsigned int caps; /* server capabilities */