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>

2 files changed, 46 insertions, 29 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;
 }
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 44f916a..7b155a0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3269,12 +3269,12 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 					size_t len,
 					unsigned int flags)
 {
-	struct page *pages[PIPE_BUFFERS];
-	struct partial_page partial[PIPE_BUFFERS];
+	struct page *pages_def[PIPE_DEF_BUFFERS];
+	struct partial_page partial_def[PIPE_DEF_BUFFERS];
 	struct trace_iterator *iter = filp->private_data;
 	struct splice_pipe_desc spd = {
-		.pages		= pages,
-		.partial	= partial,
+		.pages		= pages_def,
+		.partial	= partial_def,
 		.nr_pages	= 0, /* This gets updated below. */
 		.flags		= flags,
 		.ops		= &tracing_pipe_buf_ops,
@@ -3285,6 +3285,9 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 	size_t rem;
 	unsigned int i;
 
+	if (splice_grow_spd(pipe, &spd))
+		return -ENOMEM;
+
 	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
 	if (unlikely(old_tracer != current_trace && current_trace)) {
@@ -3315,23 +3318,23 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 	trace_access_lock(iter->cpu_file);
 
 	/* Fill as many pages as possible. */
-	for (i = 0, rem = len; i < PIPE_BUFFERS && rem; i++) {
-		pages[i] = alloc_page(GFP_KERNEL);
-		if (!pages[i])
+	for (i = 0, rem = len; i < pipe->buffers && rem; i++) {
+		spd.pages[i] = alloc_page(GFP_KERNEL);
+		if (!spd.pages[i])
 			break;
 
 		rem = tracing_fill_pipe_page(rem, iter);
 
 		/* Copy the data into the page, so we can start over. */
 		ret = trace_seq_to_buffer(&iter->seq,
-					  page_address(pages[i]),
+					  page_address(spd.pages[i]),
 					  iter->seq.len);
 		if (ret < 0) {
-			__free_page(pages[i]);
+			__free_page(spd.pages[i]);
 			break;
 		}
-		partial[i].offset = 0;
-		partial[i].len = iter->seq.len;
+		spd.partial[i].offset = 0;
+		spd.partial[i].len = iter->seq.len;
 
 		trace_seq_init(&iter->seq);
 	}
@@ -3342,12 +3345,14 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 
 	spd.nr_pages = i;
 
-	return splice_to_pipe(pipe, &spd);
+	ret = splice_to_pipe(pipe, &spd);
+out:
+	splice_shrink_spd(pipe, &spd);
+	return ret;
 
 out_err:
 	mutex_unlock(&iter->mutex);
-
-	return ret;
+	goto out;
 }
 
 static ssize_t
@@ -3746,11 +3751,11 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 			    unsigned int flags)
 {
 	struct ftrace_buffer_info *info = file->private_data;
-	struct partial_page partial[PIPE_BUFFERS];
-	struct page *pages[PIPE_BUFFERS];
+	struct partial_page partial_def[PIPE_DEF_BUFFERS];
+	struct page *pages_def[PIPE_DEF_BUFFERS];
 	struct splice_pipe_desc spd = {
-		.pages		= pages,
-		.partial	= partial,
+		.pages		= pages_def,
+		.partial	= partial_def,
 		.flags		= flags,
 		.ops		= &buffer_pipe_buf_ops,
 		.spd_release	= buffer_spd_release,
@@ -3759,22 +3764,28 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 	int entries, size, i;
 	size_t ret;
 
+	if (splice_grow_spd(pipe, &spd))
+		return -ENOMEM;
+
 	if (*ppos & (PAGE_SIZE - 1)) {
 		WARN_ONCE(1, "Ftrace: previous read must page-align\n");
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	if (len & (PAGE_SIZE - 1)) {
 		WARN_ONCE(1, "Ftrace: splice_read should page-align\n");
-		if (len < PAGE_SIZE)
-			return -EINVAL;
+		if (len < PAGE_SIZE) {
+			ret = -EINVAL;
+			goto out;
+		}
 		len &= PAGE_MASK;
 	}
 
 	trace_access_lock(info->cpu);
 	entries = ring_buffer_entries_cpu(info->tr->buffer, info->cpu);
 
-	for (i = 0; i < PIPE_BUFFERS && len && entries; i++, len -= PAGE_SIZE) {
+	for (i = 0; i < pipe->buffers && len && entries; i++, len -= PAGE_SIZE) {
 		struct page *page;
 		int r;
 
@@ -3829,11 +3840,12 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 		else
 			ret = 0;
 		/* TODO: block */
-		return ret;
+		goto out;
 	}
 
 	ret = splice_to_pipe(pipe, &spd);
-
+	splice_shrink_spd(pipe, &spd);
+out:
 	return ret;
 }