[PATCH v6 5/5] NFSD: Encode a full READ_PLUS reply

From: schumaker.anna@gmail.com
To: bfields@redhat.com, chuck.lever@oracle.com, linux-nfs@vger.kernel.org
Cc: Anna.Schumaker@Netapp.com
Subject: [PATCH v6 5/5] NFSD: Encode a full READ_PLUS reply
Date: Mon, 28 Sep 2020 13:09:01 -0400	[thread overview]
Message-ID: <20200928170901.707554-6-Anna.Schumaker@Netapp.com> (raw)
In-Reply-To: <20200928170901.707554-1-Anna.Schumaker@Netapp.com>

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

Reply to the client with multiple hole and data segments. I use the
result of the first vfs_llseek() call for encoding as an optimization so
we don't have to immediately repeat the call. This also lets us encode
any remaining reply as data if we get an unexpected result while trying
to calculate a hole.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

---
v6: Bail out of unexpected hole values by encoding the remaining reply
    as data
v5: Truncate the encode to the last segment length if we're returning a
    short read
---
 fs/nfsd/nfs4xdr.c | 49 ++++++++++++++++++++++++-----------------------
 1 file changed, 25 insertions(+), 24 deletions(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 7ed9181a69d4..dfbde8fb08f9 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -4603,16 +4603,18 @@ nfsd4_encode_offload_status(struct nfsd4_compoundres *resp, __be32 nfserr,
 static __be32
 nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
 			    struct nfsd4_read *read,
-			    unsigned long *maxcount, u32 *eof)
+			    unsigned long *maxcount, u32 *eof,
+			    loff_t *pos)
 {
 	struct xdr_stream *xdr = &resp->xdr;
 	struct file *file = read->rd_nf->nf_file;
 	int starting_len = xdr->buf->len;
-	loff_t hole_pos = vfs_llseek(file, read->rd_offset, SEEK_HOLE);
+	loff_t hole_pos;
 	__be32 nfserr;
 	__be32 *p, tmp;
 	__be64 tmp64;
 
+	hole_pos = pos ? *pos : vfs_llseek(file, read->rd_offset, SEEK_HOLE);
 	if (hole_pos > read->rd_offset)
 		*maxcount = min_t(unsigned long, *maxcount, hole_pos - read->rd_offset);
 	*maxcount = min_t(unsigned long, *maxcount, (xdr->buf->buflen - xdr->buf->len));
@@ -4647,13 +4649,14 @@ nfsd4_encode_read_plus_hole(struct nfsd4_compoundres *resp,
 {
 	struct file *file = read->rd_nf->nf_file;
 	loff_t data_pos = vfs_llseek(file, read->rd_offset, SEEK_DATA);
+	loff_t f_size = i_size_read(file_inode(file));
 	unsigned long count;
 	__be32 *p;
 
 	if (data_pos == -ENXIO)
-		data_pos = i_size_read(file_inode(file));
-	else if (data_pos <= read->rd_offset)
-		return nfserr_resource;
+		data_pos = f_size;
+	else if (data_pos <= read->rd_offset || (data_pos < f_size && data_pos % PAGE_SIZE))
+		return nfsd4_encode_read_plus_data(resp, read, maxcount, eof, &f_size);
 	count = data_pos - read->rd_offset;
 
 	/* Content type, offset, byte count */
@@ -4665,7 +4668,7 @@ nfsd4_encode_read_plus_hole(struct nfsd4_compoundres *resp,
 	 p   = xdr_encode_hyper(p, read->rd_offset);
 	 p   = xdr_encode_hyper(p, count);
 
-	*eof = (read->rd_offset + count) >= i_size_read(file_inode(file));
+	*eof = (read->rd_offset + count) >= f_size;
 	*maxcount = min_t(unsigned long, count, *maxcount);
 	return nfs_ok;
 }
@@ -4678,8 +4681,10 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
 	struct xdr_stream *xdr = &resp->xdr;
 	struct file *file;
 	int starting_len = xdr->buf->len;
+	int last_segment = xdr->buf->len;
 	int segments = 0;
 	__be32 *p, tmp;
+	bool is_data;
 	loff_t pos;
 	u32 eof;
 
@@ -4703,29 +4708,22 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
 	if (eof)
 		goto out;
 
-	pos = vfs_llseek(file, read->rd_offset, SEEK_DATA);
-	if (pos == -ENXIO)
-		pos = i_size_read(file_inode(file));
-	else if (pos < 0)
-		pos = read->rd_offset;
+	pos = vfs_llseek(file, read->rd_offset, SEEK_HOLE);
+	is_data = pos > read->rd_offset;
 
-	if (pos == read->rd_offset) {
+	while (count > 0 && !eof) {
 		maxcount = count;
-		nfserr = nfsd4_encode_read_plus_data(resp, read, &maxcount, &eof);
-		if (nfserr)
-			goto out;
-		count -= maxcount;
-		read->rd_offset += maxcount;
-		segments++;
-	}
-
-	if (count > 0 && !eof) {
-		maxcount = count;
-		nfserr = nfsd4_encode_read_plus_hole(resp, read, &maxcount, &eof);
+		if (is_data)
+			nfserr = nfsd4_encode_read_plus_data(resp, read, &maxcount, &eof,
+						segments == 0 ? &pos : NULL);
+		else
+			nfserr = nfsd4_encode_read_plus_hole(resp, read, &maxcount, &eof);
 		if (nfserr)
 			goto out;
 		count -= maxcount;
 		read->rd_offset += maxcount;
+		is_data = !is_data;
+		last_segment = xdr->buf->len;
 		segments++;
 	}
 
@@ -4737,7 +4735,10 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
 		write_bytes_to_xdr_buf(xdr->buf, starting_len,     &tmp, 4);
 		tmp = htonl(segments);
 		write_bytes_to_xdr_buf(xdr->buf, starting_len + 4, &tmp, 4);
-		nfserr = nfs_ok;
+		if (nfserr) {
+			xdr_truncate_encode(xdr, last_segment);
+			nfserr = nfs_ok;
+		}
 	}
 
 	return nfserr;
-- 
2.28.0

