[PATCH v2 2/4] NFSD: prepare nfsd_vfs_write() to use O_DIRECT on misaligned WRITEs

[Mike Snitzer <snitzer@xxxxxxxxxx>]

Refactor nfsd_vfs_write() to support splitting a WRITE into parts
(which will be either misaligned or DIO-aligned).  Doing so in a
preliminary commit just allows for indentation and slight
transformation to be more easily understood and reviewed.

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
 fs/nfsd/vfs.c | 50 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 30 insertions(+), 20 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 35c29b8ade9c3..e4855c32dad12 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1341,7 +1341,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	struct super_block	*sb = file_inode(file)->i_sb;
 	struct kiocb		kiocb;
 	struct svc_export	*exp;
-	struct iov_iter		iter;
 	errseq_t		since;
 	__be32			nfserr;
 	int			host_err;
@@ -1349,6 +1348,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	unsigned int		pflags = current->flags;
 	bool			restore_flags = false;
 	unsigned int		nvecs;
+	struct iov_iter		iter_stack[1];
+	struct iov_iter		*iter = iter_stack;
+	unsigned int		n_iters = 0;
 
 	trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
 
@@ -1378,14 +1380,15 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		kiocb.ki_flags |= IOCB_DSYNC;
 
 	nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
-	iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
+	iov_iter_bvec(&iter[0], ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
+	n_iters++;
 
 	switch (nfsd_io_cache_write) {
 	case NFSD_IO_DIRECT:
 		/* direct I/O must be aligned to device logical sector size */
 		if (nf->nf_dio_mem_align && nf->nf_dio_offset_align &&
 		    (((offset | *cnt) & (nf->nf_dio_offset_align-1)) == 0) &&
-		    iov_iter_is_aligned(&iter, nf->nf_dio_mem_align - 1,
+		    iov_iter_is_aligned(&iter[0], nf->nf_dio_mem_align - 1,
 					nf->nf_dio_offset_align - 1))
 			kiocb.ki_flags = IOCB_DIRECT;
 		break;
@@ -1396,25 +1399,32 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		break;
 	}
 
-	since = READ_ONCE(file->f_wb_err);
-	if (verf)
-		nfsd_copy_write_verifier(verf, nn);
-	host_err = vfs_iocb_iter_write(file, &kiocb, &iter);
-	if (host_err < 0) {
-		commit_reset_write_verifier(nn, rqstp, host_err);
-		goto out_nfserr;
-	}
-	*cnt = host_err;
-	nfsd_stats_io_write_add(nn, exp, *cnt);
-	fsnotify_modify(file);
-	host_err = filemap_check_wb_err(file->f_mapping, since);
-	if (host_err < 0)
-		goto out_nfserr;
+	*cnt = 0;
+	for (int i = 0; i < n_iters; i++) {
+		since = READ_ONCE(file->f_wb_err);
+		if (verf)
+			nfsd_copy_write_verifier(verf, nn);
 
-	if (stable && fhp->fh_use_wgather) {
-		host_err = wait_for_concurrent_writes(file);
-		if (host_err < 0)
+		host_err = vfs_iocb_iter_write(file, &kiocb, &iter[i]);
+		if (host_err < 0) {
 			commit_reset_write_verifier(nn, rqstp, host_err);
+			goto out_nfserr;
+		}
+		*cnt += host_err;
+		nfsd_stats_io_write_add(nn, exp, host_err);
+
+		fsnotify_modify(file);
+		host_err = filemap_check_wb_err(file->f_mapping, since);
+		if (host_err < 0)
+			goto out_nfserr;
+
+		if (stable && fhp->fh_use_wgather) {
+			host_err = wait_for_concurrent_writes(file);
+			if (host_err < 0) {
+				commit_reset_write_verifier(nn, rqstp, host_err);
+				goto out_nfserr;
+			}
+		}
 	}
 
 out_nfserr:
-- 
2.44.0