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: 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>

diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index 6c9f3f6645dd51759dd5e7e1a61abb868e038c51..7e000d782e2831fa96e63e1a3ac74e028d813715 100644 (file)
--- 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 97b386032b717a83189679ca63f265febe65b643..9723b6c533973425989cabb29ebca1052e0473f9 100644 (file)
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -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");

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 80c6ded5f74c6bfa8b74cf66b5ad629c57cc22bc..61b580bcb356dd5fc63d5c9061d436b36ee2290d 100644 (file)
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -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))

diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index e1e47ebd83ef538e0b2fd5259ac9892db407ea51..c49bfdded5c184d6770b98620f92b2cf58a55ada 100644 (file)
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -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 */