[PATCH v5 7/7] fs: add a flag for per-operation O_DSYNC semantics

[Milosz Tanski <milosz@adfin.com>]

From: Christoph Hellwig <hch@lst.de>

With the new read/write with flags syscalls we can support a flag
to enable O_DSYNC semantics on a per-operation basis.  This іs
useful to implement protocols like SMB, NFS or SCSI that have such
per-operation flags.

Example program below:

cat > pwritev2.c << EOF

        (off_t) val,                              \
        (off_t) ((((uint64_t) (val)) >> (sizeof (long) * 4)) >> (sizeof (long) * 4))

static ssize_t
pwritev2(int fd, const struct iovec *iov, int iovcnt, off_t offset, int flags)
{
        return syscall(__NR_pwritev2, fd, iov, iovcnt, LO_HI_LONG(offset),
			 flags);
}

int main(int argc, char **argv)
{
	int fd = open(argv[1], O_WRONLY|O_CREAT|O_TRUNC, 0666);
	char buf[1024];
	struct iovec iov = { .iov_base = buf, .iov_len = 1024 };
	int ret;

        if (fd < 0) {
                perror("open");
                return 0;
        }

	memset(buf, 0xfe, sizeof(buf));

	ret = pwritev2(fd, &iov, 1, 0, RWF_DSYNC);
	if (ret < 0)
		perror("pwritev2");
	else
		printf("ret = %d\n", ret);

	return 0;
}
EOF

Signed-off-by: Christoph Hellwig <hch@lst.de>
[milosz@adfin.com: added flag check to compat_do_readv_writev()]
Signed-off-by: Milosz Tanski <milosz@adfin.com>
---
 fs/ceph/file.c     |  4 +++-
 fs/fuse/file.c     |  2 ++
 fs/nfs/file.c      | 10 ++++++----
 fs/ocfs2/file.c    |  6 ++++--
 fs/read_write.c    | 20 +++++++++++++++-----
 include/linux/fs.h |  3 ++-
 mm/filemap.c       |  4 +++-
 7 files changed, 35 insertions(+), 14 deletions(-)

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index b798b5c..2d4e15a 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -983,7 +983,9 @@ retry_snap:
 	ceph_put_cap_refs(ci, got);
 
 	if (written >= 0 &&
-	    ((file->f_flags & O_SYNC) || IS_SYNC(file->f_mapping->host) ||
+	    ((file->f_flags & O_SYNC) ||
+	     IS_SYNC(file->f_mapping->host) ||
+	     (iocb->ki_rwflags & RWF_DSYNC) ||
 	     ceph_osdmap_flag(osdc->osdmap, CEPH_OSDMAP_NEARFULL))) {
 		err = vfs_fsync_range(file, pos, pos + written - 1, 1);
 		if (err < 0)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index caa8d95..bb4fb23 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1248,6 +1248,8 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		written += written_buffered;
 		iocb->ki_pos = pos + written_buffered;
 	} else {
+		if (iocb->ki_rwflags & RWF_DSYNC)
+			return -EINVAL;
 		written = fuse_perform_write(file, mapping, from, pos);
 		if (written >= 0)
 			iocb->ki_pos = pos + written;
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index aa9046f..c59b0b7 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -652,13 +652,15 @@ static const struct vm_operations_struct nfs_file_vm_ops = {
 	.remap_pages = generic_file_remap_pages,
 };
 
-static int nfs_need_sync_write(struct file *filp, struct inode *inode)
+static int nfs_need_sync_write(struct kiocb *iocb, struct inode *inode)
 {
 	struct nfs_open_context *ctx;
 
-	if (IS_SYNC(inode) || (filp->f_flags & O_DSYNC))
+	if (IS_SYNC(inode) ||
+	    (iocb->ki_filp->f_flags & O_DSYNC) ||
+	    (iocb->ki_rwflags & RWF_DSYNC))
 		return 1;
-	ctx = nfs_file_open_context(filp);
+	ctx = nfs_file_open_context(iocb->ki_filp);
 	if (test_bit(NFS_CONTEXT_ERROR_WRITE, &ctx->flags) ||
 	    nfs_ctx_key_to_expire(ctx))
 		return 1;
@@ -705,7 +707,7 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
 		written = result;
 
 	/* Return error values for O_DSYNC and IS_SYNC() */
-	if (result >= 0 && nfs_need_sync_write(file, inode)) {
+	if (result >= 0 && nfs_need_sync_write(iocb, inode)) {
 		int err = vfs_fsync(file, 0);
 		if (err < 0)
 			result = err;
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index bb66ca4..8f9a86b 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2374,8 +2374,10 @@ out_dio:
 	/* buffered aio wouldn't have proper lock coverage today */
 	BUG_ON(ret == -EIOCBQUEUED && !(file->f_flags & O_DIRECT));
 
-	if (((file->f_flags & O_DSYNC) && !direct_io) || IS_SYNC(inode) ||
-	    ((file->f_flags & O_DIRECT) && !direct_io)) {
+	if (((file->f_flags & O_DSYNC) && !direct_io) ||
+	    IS_SYNC(inode) ||
+	    ((file->f_flags & O_DIRECT) && !direct_io) ||
+	    (iocb->ki_rwflags & RWF_DSYNC)) {
 		ret = filemap_fdatawrite_range(file->f_mapping, *ppos,
 					       *ppos + count - 1);
 		if (ret < 0)
diff --git a/fs/read_write.c b/fs/read_write.c
index cba7d4c..3443265 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -839,8 +839,13 @@ static ssize_t do_readv_writev(int type, struct file *file,
 		ret = do_iter_readv_writev(file, type, iov, nr_segs, tot_len,
 						pos, iter_fn, flags);
 	} else {
-		if (type == READ && (flags & RWF_NONBLOCK))
-			return -EAGAIN;
+		if (type == READ) {
+			if (flags & RWF_NONBLOCK)
+				return -EAGAIN;
+		} else {
+			if (flags & RWF_DSYNC)
+				return -EINVAL;
+		}
 
 		if (fnv)
 			ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
@@ -888,7 +893,7 @@ ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
 		return -EBADF;
 	if (!(file->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
-	if (flags & ~0)
+	if (flags & ~RWF_DSYNC)
 		return -EINVAL;
 
 	return do_readv_writev(WRITE, file, vec, vlen, pos, flags);
@@ -1080,8 +1085,13 @@ static ssize_t compat_do_readv_writev(int type, struct file *file,
 		ret = do_iter_readv_writev(file, type, iov, nr_segs, tot_len,
 						pos, iter_fn, flags);
 	} else {
-		if (type == READ && (flags & RWF_NONBLOCK))
-			return -EAGAIN;
+		if (type == READ) {
+			if (flags & RWF_NONBLOCK)
+				return -EAGAIN;
+		} else {
+			if (flags & RWF_DSYNC)
+				return -EINVAL;
+		}
 
 		if (fnv)
 			ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7d0e116..7786b88 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1460,7 +1460,8 @@ struct block_device_operations;
 #define HAVE_UNLOCKED_IOCTL 1
 
 /* These flags are used for the readv/writev syscalls with flags. */
-#define RWF_NONBLOCK 0x00000001
+#define RWF_NONBLOCK	0x00000001
+#define RWF_DSYNC	0x00000002
 
 struct iov_iter;
 
diff --git a/mm/filemap.c b/mm/filemap.c
index 6107058..4fbef99 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2669,7 +2669,9 @@ int generic_write_sync(struct kiocb *iocb, loff_t count)
 	struct file *file = iocb->ki_filp;
 
 	if (count > 0 &&
-	    ((file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host))) {
+	    ((file->f_flags & O_DSYNC) ||
+	     (iocb->ki_rwflags & RWF_DSYNC) ||
+	     IS_SYNC(file->f_mapping->host))) {
 		bool fdatasync = !(file->f_flags & __O_SYNC);
 		ssize_t ret = 0;
 
-- 
1.9.1