[RFC PATCH 4/6] nfs/localio: add nfsd_file_dio_alignment

[Mike Snitzer <snitzer@xxxxxxxxxx>]

From: Mike Snitzer <snitzer@xxxxxxxxxxxxxxx>

And use it to avoid issuing misaligned IO using O_DIRECT.

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxxxxxxx>
---
 fs/nfs/localio.c           | 34 ++++++++++++++++++++++++++++++----
 fs/nfsd/localio.c          | 11 +++++++++++
 include/linux/nfslocalio.h |  2 ++
 3 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
index 67de26392c4a..e551690e3f6b 100644
--- a/fs/nfs/localio.c
+++ b/fs/nfs/localio.c
@@ -37,6 +37,10 @@ struct nfs_local_kiocb {
 	struct work_struct	work;
 	void (*aio_complete_work)(struct work_struct *);
 	struct nfsd_file	*localio;
+	/* local copy of nfsd_file's dio alignment attrs */
+	u32			nf_dio_mem_align;
+	u32			nf_dio_offset_align;
+	u32			nf_dio_read_offset_align;
 };
 
 struct nfs_local_fsync_ctx {
@@ -323,12 +327,10 @@ nfs_local_iocb_alloc(struct nfs_pgio_header *hdr,
 		return NULL;
 	}
 
+	init_sync_kiocb(&iocb->kiocb, file);
 	if (localio_O_DIRECT_semantics &&
-	    test_bit(NFS_IOHDR_ODIRECT, &hdr->flags)) {
-		iocb->kiocb.ki_filp = file;
+	    test_bit(NFS_IOHDR_ODIRECT, &hdr->flags))
 		iocb->kiocb.ki_flags = IOCB_DIRECT;
-	} else
-		init_sync_kiocb(&iocb->kiocb, file);
 
 	iocb->kiocb.ki_pos = hdr->args.offset;
 	iocb->hdr = hdr;
@@ -342,11 +344,29 @@ static void
 nfs_local_iter_init(struct iov_iter *i, struct nfs_local_kiocb *iocb, int dir)
 {
 	struct nfs_pgio_header *hdr = iocb->hdr;
+	u32 nf_dio_mem_align, nf_dio_offset_align;
+
+	if (iocb->kiocb.ki_flags & IOCB_DIRECT) {
+		nf_dio_mem_align = iocb->nf_dio_mem_align;
+		if (dir == READ)
+			nf_dio_offset_align = iocb->nf_dio_read_offset_align;
+		else
+			nf_dio_offset_align = iocb->nf_dio_offset_align;
+	}
 
 	iov_iter_bvec(i, dir, iocb->bvec, hdr->page_array.npages,
 		      hdr->args.count + hdr->args.pgbase);
 	if (hdr->args.pgbase != 0)
 		iov_iter_advance(i, hdr->args.pgbase);
+	/* Verify the IO is DIO-aligned as needed */
+	if (iocb->kiocb.ki_flags & IOCB_DIRECT &&
+	    !iov_iter_is_aligned(i, nf_dio_mem_align - 1,
+				 nf_dio_offset_align - 1)) {
+		/* Fallback to buffered IO */
+		iocb->kiocb.ki_flags &= ~IOCB_DIRECT;
+		iocb->kiocb.ki_complete = NULL;
+		iocb->aio_complete_work = NULL;
+	}
 }
 
 static void
@@ -481,6 +501,9 @@ nfs_do_local_read(struct nfs_pgio_header *hdr,
 	if (iocb == NULL)
 		return -ENOMEM;
 	iocb->localio = localio;
+	nfs_to->nfsd_file_dio_alignment(localio, &iocb->nf_dio_mem_align,
+					&iocb->nf_dio_offset_align,
+					&iocb->nf_dio_read_offset_align);
 
 	nfs_local_pgio_init(hdr, call_ops);
 	hdr->res.eof = false;
@@ -680,6 +703,9 @@ nfs_do_local_write(struct nfs_pgio_header *hdr,
 	if (iocb == NULL)
 		return -ENOMEM;
 	iocb->localio = localio;
+	nfs_to->nfsd_file_dio_alignment(localio, &iocb->nf_dio_mem_align,
+					&iocb->nf_dio_offset_align,
+					&iocb->nf_dio_read_offset_align);
 
 	switch (hdr->args.stable) {
 	default:
diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c
index 4f6468eb2adf..3eb1997289fe 100644
--- a/fs/nfsd/localio.c
+++ b/fs/nfsd/localio.c
@@ -116,6 +116,16 @@ nfsd_open_local_fh(struct net *net, struct auth_domain *dom,
 	return localio;
 }
 
+static void nfsd_file_dio_alignment(struct nfsd_file *nf,
+				    u32 *nf_dio_mem_align,
+				    u32 *nf_dio_offset_align,
+				    u32 *nf_dio_read_offset_align)
+{
+	*nf_dio_mem_align = nf->nf_dio_mem_align;
+	*nf_dio_offset_align = nf->nf_dio_offset_align;
+	*nf_dio_read_offset_align = nf->nf_dio_read_offset_align;
+}
+
 static const struct nfsd_localio_operations nfsd_localio_ops = {
 	.nfsd_net_try_get  = nfsd_net_try_get,
 	.nfsd_net_put  = nfsd_net_put,
@@ -123,6 +133,7 @@ static const struct nfsd_localio_operations nfsd_localio_ops = {
 	.nfsd_file_put_local = nfsd_file_put_local,
 	.nfsd_file_get_local = nfsd_file_get_local,
 	.nfsd_file_file = nfsd_file_file,
+	.nfsd_file_dio_alignment = nfsd_file_dio_alignment,
 };
 
 void nfsd_localio_ops_init(void)
diff --git a/include/linux/nfslocalio.h b/include/linux/nfslocalio.h
index 453d9de3d70b..f9d07fef7dba 100644
--- a/include/linux/nfslocalio.h
+++ b/include/linux/nfslocalio.h
@@ -65,6 +65,8 @@ struct nfsd_localio_operations {
 	struct net *(*nfsd_file_put_local)(struct nfsd_file *);
 	struct nfsd_file *(*nfsd_file_get_local)(struct nfsd_file *);
 	struct file *(*nfsd_file_file)(struct nfsd_file *);
+	void (*nfsd_file_dio_alignment)(struct nfsd_file *,
+					u32 *, u32 *, u32 *);
 } ____cacheline_aligned;
 
 extern void nfsd_localio_ops_init(void);
-- 
2.44.0