On Thu, 2024-06-27 at 13:01 +0300, Dan Aloni wrote:
> 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@xxxxxxxxxxxx>
> ---
> fs/nfs/fs_context.c | 8 ++++++++
> fs/nfs/super.c | 3 +++
> fs/nfs/write.c | 3 +++
> include/linux/nfs_fs_sb.h | 1 +
> 4 files changed, 15 insertions(+)
>
> diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
> index 6c9f3f6645dd..7e000d782e28 100644
> --- a/fs/nfs/fs_context.c
> +++ b/fs/nfs/fs_context.c
> @@ -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;
> diff --git a/fs/nfs/super.c b/fs/nfs/super.c
> index cbbd4866b0b7..1382ae19bba4 100644
> --- a/fs/nfs/super.c
> +++ b/fs/nfs/super.c
> @@ -549,6 +549,9 @@ 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");
> diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> index 2329cbb0e446..cfe8061bf005 100644
> --- a/fs/nfs/write.c
> +++ b/fs/nfs/write.c
> @@ -1315,7 +1315,10 @@ 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))
> diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
> index 92de074e63b9..4d28b4a328a7 100644
> --- a/include/linux/nfs_fs_sb.h
> +++ b/include/linux/nfs_fs_sb.h
> @@ -157,6 +157,7 @@ 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 */
While I hate that we need a new mount option for this, I do understand
the need. I do wonder if we'd be better served by a new fadvise64()
flag or something. Either way, this would probably be needed in the
interim, so...
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
