From 9f0b5792f07d8f0745c3620d577d6930ff2a96fd Mon Sep 17 00:00:00 2001
From: Anna Schumaker <Anna.Schumaker@Netapp.com>
Date: Mon, 28 Sep 2020 13:09:01 -0400
Subject: [PATCH] NFSD: Encode a full READ_PLUS reply

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>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 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 2aff50745d6d..833a2c64dfe8 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 @@ out:
 		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;