diff options
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/pipe.c | 61 | ||||
| -rw-r--r-- | fs/splice.c | 4 |
2 files changed, 64 insertions, 1 deletions
diff --git a/fs/pipe.c b/fs/pipe.c index 3694af10dd2..d007830d9c8 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -164,6 +164,20 @@ static void anon_pipe_buf_release(struct pipe_inode_info *pipe, page_cache_release(page); } +/** + * generic_pipe_buf_map - virtually map a pipe buffer + * @pipe: the pipe that the buffer belongs to + * @buf: the buffer that should be mapped + * @atomic: whether to use an atomic map + * + * Description: + * This function returns a kernel virtual address mapping for the + * passed in @pipe_buffer. If @atomic is set, an atomic map is provided + * and the caller has to be careful not to fault before calling + * the unmap function. + * + * Note that this function occupies KM_USER0 if @atomic != 0. + */ void *generic_pipe_buf_map(struct pipe_inode_info *pipe, struct pipe_buffer *buf, int atomic) { @@ -175,6 +189,15 @@ void *generic_pipe_buf_map(struct pipe_inode_info *pipe, return kmap(buf->page); } +/** + * generic_pipe_buf_unmap - unmap a previously mapped pipe buffer + * @pipe: the pipe that the buffer belongs to + * @buf: the buffer that should be unmapped + * @map_data: the data that the mapping function returned + * + * Description: + * This function undoes the mapping that ->map() provided. + */ void generic_pipe_buf_unmap(struct pipe_inode_info *pipe, struct pipe_buffer *buf, void *map_data) { @@ -185,11 +208,28 @@ void generic_pipe_buf_unmap(struct pipe_inode_info *pipe, kunmap(buf->page); } +/** + * generic_pipe_buf_steal - attempt to take ownership of a @pipe_buffer + * @pipe: the pipe that the buffer belongs to + * @buf: the buffer to attempt to steal + * + * Description: + * This function attempts to steal the @struct page attached to + * @buf. If successful, this function returns 0 and returns with + * the page locked. The caller may then reuse the page for whatever + * he wishes, the typical use is insertion into a different file + * page cache. + */ int generic_pipe_buf_steal(struct pipe_inode_info *pipe, struct pipe_buffer *buf) { struct page *page = buf->page; + /* + * A reference of one is golden, that means that the owner of this + * page is the only one holding a reference to it. lock the page + * and return OK. + */ if (page_count(page) == 1) { lock_page(page); return 0; @@ -198,11 +238,30 @@ int generic_pipe_buf_steal(struct pipe_inode_info *pipe, return 1; } -void generic_pipe_buf_get(struct pipe_inode_info *info, struct pipe_buffer *buf) +/** + * generic_pipe_buf_get - get a reference to a @struct pipe_buffer + * @pipe: the pipe that the buffer belongs to + * @buf: the buffer to get a reference to + * + * Description: + * This function grabs an extra reference to @buf. It's used in + * in the tee() system call, when we duplicate the buffers in one + * pipe into another. + */ +void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf) { page_cache_get(buf->page); } +/** + * generic_pipe_buf_confirm - verify contents of the pipe buffer + * @pipe: the pipe that the buffer belongs to + * @buf: the buffer to confirm + * + * Description: + * This function does nothing, because the generic pipe code uses + * pages that are always good when inserted into the pipe. + */ int generic_pipe_buf_confirm(struct pipe_inode_info *info, struct pipe_buffer *buf) { diff --git a/fs/splice.c b/fs/splice.c index c804121601b..ed2ce995475 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -85,6 +85,10 @@ static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe, buf->flags &= ~PIPE_BUF_FLAG_LRU; } +/* + * Check whether the contents of buf is OK to access. Since the content + * is a page cache page, IO may be in flight. + */ static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe, struct pipe_buffer *buf) { |