Commit dfb07e99 authored by Dan Aloni's avatar Dan Aloni Committed by Anna Schumaker
Browse files

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



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: default avatarDan Aloni <dan.aloni@vastdata.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Reviewed-by: default avatarSagi Grimberg <sagi@grimberg.me>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAnna Schumaker <anna.schumaker@oracle.com>
parent 6d26c5e4

fs/nfs/fs_context.c

+8 −0
Original line number Diff line number Diff line
@@ -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;

fs/nfs/super.c

+3 −0
Original line number Diff line number Diff line
@@ -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");

fs/nfs/write.c

+3 −0
Original line number Diff line number Diff line
@@ -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))

include/linux/nfs_fs_sb.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */