linux-kernel - [RFC PATCH 5/8] relay - Map the first sub-buffer at the end of the buffer, for temporary convenience.

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Date:	Thu, 25 Sep 2008 01:07:47 -0500
From:	Tom Zanussi <zanussi@...cast.net>
To:	Martin Bligh <mbligh@...gle.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, prasad@...ux.vnet.ibm.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Steven Rostedt <rostedt@...dmis.org>, od@...e.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, hch@....de,
	David Wilder <dwilder@...ibm.com>
Subject: [RFC PATCH 5/8] relay - Map the first sub-buffer at the end of the
	buffer, for temporary convenience.

Map the first sub-buffer at the end of the buffer, for temporary convenience.

Make relay buffers 'circular' for writing by mapping the first subbuf
at end of last subbuf.  This is so we can do writes across last subbuf
boundary without adding special write logic.  This is a temporary
state of affairs and it all goes away in a future patch, but it's here
now so things will still work.
---
 kernel/relay.c |   26 +++++++++++++++-----------
 1 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/kernel/relay.c b/kernel/relay.c
index 9ea9240..9a08fec 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -125,20 +125,20 @@ static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
 /**
  *	relay_alloc_buf - allocate a channel buffer
  *	@buf: the buffer struct
- *	@size: total size of the buffer
  *
  *	Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
  *	passed in size will get page aligned, if it isn't already.
  */
-static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
+static void *relay_alloc_buf(struct rchan_buf *buf)
 {
 	void *mem;
-	unsigned int i, j, n_pages;
+	unsigned int i, j, n_pages, n_subbuf_pages;
 
-	*size = PAGE_ALIGN(*size);
-	n_pages = *size >> PAGE_SHIFT;
+	buf->chan->alloc_size = PAGE_ALIGN(buf->chan->alloc_size);
+	n_pages = buf->chan->alloc_size >> PAGE_SHIFT;
+	n_subbuf_pages = PAGE_ALIGN(buf->chan->subbuf_size) >> PAGE_SHIFT;
 
-	buf->page_array = relay_alloc_page_array(n_pages);
+	buf->page_array = relay_alloc_page_array(n_pages + n_subbuf_pages);
 	if (!buf->page_array)
 		return NULL;
 
@@ -148,11 +148,14 @@ static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
 			goto depopulate;
 		set_page_private(buf->page_array[i], (unsigned long)buf);
 	}
-	mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
+	for (i = 0; i < n_subbuf_pages; i++)
+		buf->page_array[n_pages + i] = buf->page_array[i];
+	mem = vmap(buf->page_array, n_pages + n_subbuf_pages, VM_MAP,
+		   PAGE_KERNEL);
 	if (!mem)
 		goto depopulate;
 
-	memset(mem, 0, *size);
+	memset(mem, 0, buf->chan->alloc_size);
 	buf->page_count = n_pages;
 	return mem;
 
@@ -179,12 +182,13 @@ static struct rchan_buf *relay_create_buf(struct rchan *chan)
 	if (!buf->padding)
 		goto free_buf;
 
-	buf->start = relay_alloc_buf(buf, &chan->alloc_size);
+	buf->chan = chan;
+	kref_get(&buf->chan->kref);
+
+	buf->start = relay_alloc_buf(buf);
 	if (!buf->start)
 		goto free_buf;
 
-	buf->chan = chan;
-	kref_get(&buf->chan->kref);
 	return buf;
 
 free_buf:
-- 
1.5.3.5



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