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virtio/console: Add a failback for unstealable pipe buffer 

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@hitachi.com>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Masami Hiramatsu 2012-08-09 21:30:50 +09:00 committed by Rusty Russell
parent eb5e89fc70
commit ec8fc87015
1 changed files with 25 additions and 3 deletions
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28
drivers/char/virtio_console.c
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@ -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;
}