pipe: add support for shrinking and growing pipes

This patch adds F_GETPIPE_SZ and F_SETPIPE_SZ fcntl() actions for
growing and shrinking the size of a pipe and adjusts pipe.c and splice.c
(and relay and network splice) usage to work with these larger (or smaller)
pipes.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/kernel/relay.c b/kernel/relay.c
index 3d97f28..4268287 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -1231,8 +1231,8 @@ static ssize_t subbuf_splice_actor(struct file *in,
 	size_t read_subbuf = read_start / subbuf_size;
 	size_t padding = rbuf->padding[read_subbuf];
 	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
-	struct page *pages[PIPE_BUFFERS];
-	struct partial_page partial[PIPE_BUFFERS];
+	struct page *pages[PIPE_DEF_BUFFERS];
+	struct partial_page partial[PIPE_DEF_BUFFERS];
 	struct splice_pipe_desc spd = {
 		.pages = pages,
 		.nr_pages = 0,
@@ -1245,6 +1245,8 @@ static ssize_t subbuf_splice_actor(struct file *in,
 
 	if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
 		return 0;
+	if (splice_grow_spd(pipe, &spd))
+		return -ENOMEM;
 
 	/*
 	 * Adjust read len, if longer than what is available
@@ -1255,7 +1257,7 @@ static ssize_t subbuf_splice_actor(struct file *in,
 	subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
 	pidx = (read_start / PAGE_SIZE) % subbuf_pages;
 	poff = read_start & ~PAGE_MASK;
-	nr_pages = min_t(unsigned int, subbuf_pages, PIPE_BUFFERS);
+	nr_pages = min_t(unsigned int, subbuf_pages, pipe->buffers);
 
 	for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
 		unsigned int this_len, this_end, private;
@@ -1289,16 +1291,19 @@ static ssize_t subbuf_splice_actor(struct file *in,
 		}
 	}
 
+	ret = 0;
 	if (!spd.nr_pages)
-		return 0;
+		goto out;
 
 	ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
 	if (ret < 0 || ret < total_len)
-		return ret;
+		goto out;
 
         if (read_start + ret == nonpad_end)
                 ret += padding;
 
+out:
+	splice_shrink_spd(pipe, &spd);
         return ret;
 }