diff options
| -rw-r--r-- | fs/pipe.c | 61 | ||||
| -rw-r--r-- | fs/splice.c | 4 | ||||
| -rw-r--r-- | include/linux/pipe_fs_i.h | 77 |
3 files changed, 140 insertions, 2 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) { diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h index cc09fe89bf0..8e4120285f7 100644 --- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -9,6 +9,15 @@ #define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */ #define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */ +/** + * struct pipe_buffer - a linux kernel pipe buffer + * @page: the page containing the data for the pipe buffer + * @offset: offset of data inside the @page + * @len: length of data inside the @page + * @ops: operations associated with this buffer. See @pipe_buf_operations. + * @flags: pipe buffer flags. See above. + * @private: private data owned by the ops. + **/ struct pipe_buffer { struct page *page; unsigned int offset, len; @@ -17,6 +26,22 @@ struct pipe_buffer { unsigned long private; }; +/** + * struct pipe_inode_info - a linux kernel pipe + * @wait: reader/writer wait point in case of empty/full pipe + * @nrbufs: the number of non-empty pipe buffers in this pipe + * @curbuf: the current pipe buffer entry + * @tmp_page: cached released page + * @readers: number of current readers of this pipe + * @writers: number of current writers of this pipe + * @waiting_writers: number of writers blocked waiting for room + * @r_counter: reader counter + * @w_counter: writer counter + * @fasync_readers: reader side fasync + * @fasync_writers: writer side fasync + * @inode: inode this pipe is attached to + * @bufs: the circular array of pipe buffers + **/ struct pipe_inode_info { wait_queue_head_t wait; unsigned int nrbufs, curbuf; @@ -43,15 +68,65 @@ struct pipe_inode_info { * ->unmap() * * That is, ->map() must be called on a confirmed buffer, - * same goes for ->steal(). + * same goes for ->steal(). See below for the meaning of each + * operation. Also see kerneldoc in fs/pipe.c for the pipe + * and generic variants of these hooks. */ struct pipe_buf_operations { + /* + * This is set to 1, if the generic pipe read/write may coalesce + * data into an existing buffer. If this is set to 0, a new pipe + * page segment is always used for new data. + */ int can_merge; + + /* + * ->map() returns a virtual address mapping of the pipe buffer. + * The last integer flag reflects whether this should be an atomic + * mapping or not. The atomic map is faster, however you can't take + * page faults before calling ->unmap() again. So if you need to eg + * access user data through copy_to/from_user(), then you must get + * a non-atomic map. ->map() uses the KM_USER0 atomic slot for + * atomic maps, so you can't map more than one pipe_buffer at once + * and you have to be careful if mapping another page as source + * or destination for a copy (IOW, it has to use something else + * than KM_USER0). + */ void * (*map)(struct pipe_inode_info *, struct pipe_buffer *, int); + + /* + * Undoes ->map(), finishes the virtual mapping of the pipe buffer. + */ void (*unmap)(struct pipe_inode_info *, struct pipe_buffer *, void *); + + /* + * ->confirm() verifies that the data in the pipe buffer is there + * and that the contents are good. If the pages in the pipe belong + * to a file system, we may need to wait for IO completion in this + * hook. Returns 0 for good, or a negative error value in case of + * error. + */ int (*confirm)(struct pipe_inode_info *, struct pipe_buffer *); + + /* + * When the contents of this pipe buffer has been completely + * consumed by a reader, ->release() is called. + */ void (*release)(struct pipe_inode_info *, struct pipe_buffer *); + + /* + * Attempt to take ownership of the pipe buffer and its contents. + * ->steal() returns 0 for success, in which case the contents + * of the pipe (the buf->page) is locked and now completely owned + * by the caller. The page may then be transferred to a different + * mapping, the most often used case is insertion into different + * file address space cache. + */ int (*steal)(struct pipe_inode_info *, struct pipe_buffer *); + + /* + * Get a reference to the pipe buffer. + */ void (*get)(struct pipe_inode_info *, struct pipe_buffer *); }; |