diff options
| -rw-r--r-- | fs/splice.c | 70 |
1 files changed, 66 insertions, 4 deletions
diff --git a/fs/splice.c b/fs/splice.c index 07f4d863c2d4..34591924c783 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -37,6 +37,12 @@ struct splice_desc { loff_t pos; /* file position */ }; +/* + * Attempt to steal a page from a pipe buffer. This should perhaps go into + * a vm helper function, it's already simplified quite a bit by the + * addition of remove_mapping(). If success is returned, the caller may + * attempt to reuse this page for another destination. + */ static int page_cache_pipe_buf_steal(struct pipe_inode_info *info, struct pipe_buffer *buf) { @@ -108,6 +114,10 @@ static struct pipe_buf_operations page_cache_pipe_buf_ops = { .steal = page_cache_pipe_buf_steal, }; +/* + * Pipe output worker. This sets up our pipe format with the page cache + * pipe buffer operations. Otherwise very similar to the regular pipe_writev(). + */ static ssize_t move_to_pipe(struct inode *inode, struct page **pages, int nr_pages, unsigned long offset, unsigned long len, unsigned int flags) @@ -292,6 +302,16 @@ splice_them: return move_to_pipe(pipe, pages, i, offset, len, flags); } +/** + * generic_file_splice_read - splice data from file to a pipe + * @in: file to splice from + * @pipe: pipe to splice to + * @len: number of bytes to splice + * @flags: splice modifier flags + * + * Will read pages from given file and fill them into a pipe. + * + */ ssize_t generic_file_splice_read(struct file *in, struct inode *pipe, size_t len, unsigned int flags) { @@ -370,10 +390,12 @@ static int pipe_to_sendpage(struct pipe_inode_info *info, * - Destination page does not exist, we can add the pipe page to * the page cache and avoid the copy. * - * For now we just do the slower thing and always copy pages over, it's - * easier than migrating pages from the pipe to the target file. For the - * case of doing file | file splicing, the migrate approach had some LRU - * nastiness... + * If asked to move pages to the output file (SPLICE_F_MOVE is set in + * sd->flags), we attempt to migrate pages from the pipe to the output + * file address space page cache. This is possible if no one else has + * the pipe page referenced outside of the pipe and page cache. If + * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create + * a new page in the output file page cache and fill/dirty that. */ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf, struct splice_desc *sd) @@ -401,6 +423,10 @@ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf, * reuse buf page, if SPLICE_F_MOVE is set */ if (sd->flags & SPLICE_F_MOVE) { + /* + * If steal succeeds, buf->page is now pruned from the vm + * side (LRU and page cache) and we can reuse it. + */ if (buf->ops->steal(info, buf)) goto find_page; @@ -484,6 +510,11 @@ out: typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *, struct splice_desc *); +/* + * Pipe input worker. Most of this logic works like a regular pipe, the + * key here is the 'actor' worker passed in that actually moves the data + * to the wanted destination. See pipe_to_file/pipe_to_sendpage above. + */ static ssize_t move_from_pipe(struct inode *inode, struct file *out, size_t len, unsigned int flags, splice_actor *actor) @@ -585,6 +616,17 @@ static ssize_t move_from_pipe(struct inode *inode, struct file *out, } +/** + * generic_file_splice_write - splice data from a pipe to a file + * @inode: pipe inode + * @out: file to write to + * @len: number of bytes to splice + * @flags: splice modifier flags + * + * Will either move or copy pages (determined by @flags options) from + * the given pipe inode to the given file. + * + */ ssize_t generic_file_splice_write(struct inode *inode, struct file *out, size_t len, unsigned int flags) { @@ -611,6 +653,17 @@ ssize_t generic_file_splice_write(struct inode *inode, struct file *out, return ret; } +/** + * generic_splice_sendpage - splice data from a pipe to a socket + * @inode: pipe inode + * @out: socket to write to + * @len: number of bytes to splice + * @flags: splice modifier flags + * + * Will send @len bytes from the pipe to a network socket. No data copying + * is involved. + * + */ ssize_t generic_splice_sendpage(struct inode *inode, struct file *out, size_t len, unsigned int flags) { @@ -620,6 +673,9 @@ ssize_t generic_splice_sendpage(struct inode *inode, struct file *out, EXPORT_SYMBOL(generic_file_splice_write); EXPORT_SYMBOL(generic_file_splice_read); +/* + * Attempt to initiate a splice from pipe to file. + */ static long do_splice_from(struct inode *pipe, struct file *out, size_t len, unsigned int flags) { @@ -640,6 +696,9 @@ static long do_splice_from(struct inode *pipe, struct file *out, size_t len, return out->f_op->splice_write(pipe, out, len, flags); } +/* + * Attempt to initiate a splice from a file to a pipe. + */ static long do_splice_to(struct file *in, struct inode *pipe, size_t len, unsigned int flags) { @@ -668,6 +727,9 @@ static long do_splice_to(struct file *in, struct inode *pipe, size_t len, return in->f_op->splice_read(in, pipe, len, flags); } +/* + * Determine where to splice to/from. + */ static long do_splice(struct file *in, struct file *out, size_t len, unsigned int flags) { |