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ITER_PIPE: helpers for adding pipe buffers

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There are only two kinds of pipe_buffer in the area used by ITER_PIPE.

1) anonymous - copy_to_iter() et.al. end up creating those and copying
data there.  They have zero ->offset, and their ->ops points to
default_pipe_page_ops.

2) zero-copy ones - those come from copy_page_to_iter(), and page
comes from caller.  ->offset is also caller-supplied - it might be
non-zero.  ->ops points to page_cache_pipe_buf_ops.

Move creation and insertion of those into helpers - push_anon(pipe, size)
and push_page(pipe, page, offset, size) resp., separating them from
the "could we avoid creating a new buffer by merging with the current
head?" logics.

Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2022-06-13 14:30:15 -04:00
parent 2dcedb2a54
commit 47b7fcae41
1 changed files with 46 additions and 42 deletions
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88
lib/iov_iter.c
View File

@ -231,15 +231,39 @@ Bad:
#define sanity(i) true
#endif
static struct page *push_anon(struct pipe_inode_info *pipe, unsigned size)
{
struct page *page = alloc_page(GFP_USER);
if (page) {
struct pipe_buffer *buf = pipe_buf(pipe, pipe->head++);
*buf = (struct pipe_buffer) {
.ops = &default_pipe_buf_ops,
.page = page,
.offset = 0,
.len = size
};
}
return page;
}
static void push_page(struct pipe_inode_info *pipe, struct page *page,
unsigned int offset, unsigned int size)
{
struct pipe_buffer *buf = pipe_buf(pipe, pipe->head++);
*buf = (struct pipe_buffer) {
.ops = &page_cache_pipe_buf_ops,
.page = page,
.offset = offset,
.len = size
};
get_page(page);
}
static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t bytes,
struct iov_iter *i)
{
struct pipe_inode_info *pipe = i->pipe;
struct pipe_buffer *buf;
unsigned int p_tail = pipe->tail;
unsigned int p_mask = pipe->ring_size - 1;
unsigned int i_head = i->head;
size_t off;
unsigned int head = pipe->head;
if (unlikely(bytes > i->count))
bytes = i->count;
@ -250,32 +274,21 @@ static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t by
if (!sanity(i))
return 0;
off = i->iov_offset;
buf = &pipe->bufs[i_head & p_mask];
if (off) {
if (offset == off && buf->page == page) {
/* merge with the last one */
if (offset && i->iov_offset == offset) { // could we merge it?
struct pipe_buffer *buf = pipe_buf(pipe, head - 1);
if (buf->page == page) {
buf->len += bytes;
i->iov_offset += bytes;
goto out;
i->count -= bytes;
return bytes;
}
i_head++;
buf = &pipe->bufs[i_head & p_mask];
}
if (pipe_full(i_head, p_tail, pipe->max_usage))
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
return 0;
buf->ops = &page_cache_pipe_buf_ops;
buf->flags = 0;
get_page(page);
buf->page = page;
buf->offset = offset;
buf->len = bytes;
pipe->head = i_head + 1;
push_page(pipe, page, offset, bytes);
i->iov_offset = offset + bytes;
i->head = i_head;
out:
i->head = head;
i->count -= bytes;
return bytes;
}
@ -407,8 +420,6 @@ static size_t push_pipe(struct iov_iter *i, size_t size,
int *iter_headp, size_t *offp)
{
struct pipe_inode_info *pipe = i->pipe;
unsigned int p_tail = pipe->tail;
unsigned int p_mask = pipe->ring_size - 1;
unsigned int iter_head;
size_t off;
ssize_t left;
@ -423,30 +434,23 @@ static size_t push_pipe(struct iov_iter *i, size_t size,
*iter_headp = iter_head;
*offp = off;
if (off) {
struct pipe_buffer *buf = pipe_buf(pipe, iter_head);
left -= PAGE_SIZE - off;
if (left <= 0) {
pipe->bufs[iter_head & p_mask].len += size;
buf->len += size;
return size;
}
pipe->bufs[iter_head & p_mask].len = PAGE_SIZE;
iter_head++;
buf->len = PAGE_SIZE;
}
while (!pipe_full(iter_head, p_tail, pipe->max_usage)) {
struct pipe_buffer *buf = &pipe->bufs[iter_head & p_mask];
struct page *page = alloc_page(GFP_USER);
while (!pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
struct page *page = push_anon(pipe,
min_t(ssize_t, left, PAGE_SIZE));
if (!page)
break;
buf->ops = &default_pipe_buf_ops;
buf->flags = 0;
buf->page = page;
buf->offset = 0;
buf->len = min_t(ssize_t, left, PAGE_SIZE);
left -= buf->len;
iter_head++;
pipe->head = iter_head;
if (left == 0)
left -= PAGE_SIZE;
if (left <= 0)
return size;
}
return size - left;