[PATCH V2 2/6] virtio/console: Add a failback for unstealable pipe buffer
From: Yoshihiro YUNOMAE <hidden>
Date: 2012-08-09 12:31:06
Also in:
lkml, qemu-devel
Subsystem:
char and misc drivers, the rest, virtio console driver · Maintainers:
Arnd Bergmann, Greg Kroah-Hartman, Linus Torvalds, Amit Shah
From: Masami Hiramatsu <redacted> 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 <redacted> --- 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; }