linux-kernel - [PATCH V2 2/6] virtio/console: Add a failback for unstealable pipe buffer

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Message-ID: <20120809123049.8542.21179.stgit@ltc189.sdl.hitachi.co.jp>
Date:	Thu, 09 Aug 2012 21:30:50 +0900
From:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
To:	linux-kernel@...r.kernel.org
Cc:	Amit Shah <amit.shah@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...64.org>,
	"Franch Ch. Eigler" <fche@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ingo Molnar <mingo@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	virtualization@...ts.linux-foundation.org, qemu-devel@...gnu.org,
	yrl.pp-manager.tt@...achi.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: [PATCH V2 2/6] virtio/console: Add a failback for unstealable pipe
 buffer

From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Add a failback memcpy path for unstealable pipe buffer.
If buf->ops->steal() fails, virtio-serial tries to
copy the page contents to an allocated page, instead
of just failing splice().

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
---

 drivers/char/virtio_console.c |   28 +++++++++++++++++++++++++---
 1 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 730816c..22b7373 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -794,7 +794,7 @@ static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 			struct splice_desc *sd)
 {
 	struct sg_list *sgl = sd->u.data;
-	unsigned int len = 0;
+	unsigned int offset, len;
 
 	if (sgl->n == MAX_SPLICE_PAGES)
 		return 0;
@@ -807,9 +807,31 @@ static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 
 		len = min(buf->len, sd->len);
 		sg_set_page(&(sgl->sg[sgl->n]), buf->page, len, buf->offset);
-		sgl->n++;
-		sgl->len += len;
+	} else {
+		/* Failback to copying a page */
+		struct page *page = alloc_page(GFP_KERNEL);
+		char *src = buf->ops->map(pipe, buf, 1);
+		char *dst;
+
+		if (!page)
+			return -ENOMEM;
+		dst = kmap(page);
+
+		offset = sd->pos & ~PAGE_MASK;
+
+		len = sd->len;
+		if (len + offset > PAGE_SIZE)
+			len = PAGE_SIZE - offset;
+
+		memcpy(dst + offset, src + buf->offset, len);
+
+		kunmap(page);
+		buf->ops->unmap(pipe, buf, src);
+
+		sg_set_page(&(sgl->sg[sgl->n]), page, len, offset);
 	}
+	sgl->n++;
+	sgl->len += len;
 
 	return len;
 }


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