[PATCH] Introduce sys_splice() system call
This adds support for the sys_splice system call. Using a pipe as a
transport, it can connect to files or sockets (latter as output only).
From the splice.c comments:
"splice": joining two ropes together by interweaving their strands.
This is the "extended pipe" functionality, where a pipe is used as
an arbitrary in-memory buffer. Think of a pipe as a small kernel
buffer that you can use to transfer data from one end to the other.
The traditional unix read/write is extended with a "splice()" operation
that transfers data buffers to or from a pipe buffer.
Named by Larry McVoy, original implementation from Linus, extended by
Jens to support splicing to files and fixing the initial implementation
bugs.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/splice.c b/fs/splice.c
new file mode 100644
index 0000000..efa47c1
--- /dev/null
+++ b/fs/splice.c
@@ -0,0 +1,612 @@
+/*
+ * "splice": joining two ropes together by interweaving their strands.
+ *
+ * This is the "extended pipe" functionality, where a pipe is used as
+ * an arbitrary in-memory buffer. Think of a pipe as a small kernel
+ * buffer that you can use to transfer data from one end to the other.
+ *
+ * The traditional unix read/write is extended with a "splice()" operation
+ * that transfers data buffers to or from a pipe buffer.
+ *
+ * Named by Larry McVoy, original implementation from Linus, extended by
+ * Jens to support splicing to files and fixing the initial implementation
+ * bugs.
+ *
+ * Copyright (C) 2005 Jens Axboe <axboe@suse.de>
+ * Copyright (C) 2005 Linus Torvalds <torvalds@osdl.org>
+ *
+ */
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/pagemap.h>
+#include <linux/pipe_fs_i.h>
+#include <linux/mm_inline.h>
+
+/*
+ * Passed to the actors
+ */
+struct splice_desc {
+ unsigned int len, total_len; /* current and remaining length */
+ unsigned int flags; /* splice flags */
+ struct file *file; /* file to read/write */
+ loff_t pos; /* file position */
+};
+
+static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
+ struct pipe_buffer *buf)
+{
+ page_cache_release(buf->page);
+ buf->page = NULL;
+}
+
+static void *page_cache_pipe_buf_map(struct file *file,
+ struct pipe_inode_info *info,
+ struct pipe_buffer *buf)
+{
+ struct page *page = buf->page;
+
+ lock_page(page);
+
+ if (!PageUptodate(page)) {
+ unlock_page(page);
+ return ERR_PTR(-EIO);
+ }
+
+ if (!page->mapping) {
+ unlock_page(page);
+ return ERR_PTR(-ENODATA);
+ }
+
+ return kmap(buf->page);
+}
+
+static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
+ struct pipe_buffer *buf)
+{
+ unlock_page(buf->page);
+ kunmap(buf->page);
+}
+
+static struct pipe_buf_operations page_cache_pipe_buf_ops = {
+ .can_merge = 0,
+ .map = page_cache_pipe_buf_map,
+ .unmap = page_cache_pipe_buf_unmap,
+ .release = page_cache_pipe_buf_release,
+};
+
+static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
+ int nr_pages, unsigned long offset,
+ unsigned long len)
+{
+ struct pipe_inode_info *info;
+ int ret, do_wakeup, i;
+
+ ret = 0;
+ do_wakeup = 0;
+ i = 0;
+
+ mutex_lock(PIPE_MUTEX(*inode));
+
+ info = inode->i_pipe;
+ for (;;) {
+ int bufs;
+
+ if (!PIPE_READERS(*inode)) {
+ send_sig(SIGPIPE, current, 0);
+ if (!ret)
+ ret = -EPIPE;
+ break;
+ }
+
+ bufs = info->nrbufs;
+ if (bufs < PIPE_BUFFERS) {
+ int newbuf = (info->curbuf + bufs) & (PIPE_BUFFERS - 1);
+ struct pipe_buffer *buf = info->bufs + newbuf;
+ struct page *page = pages[i++];
+ unsigned long this_len;
+
+ this_len = PAGE_CACHE_SIZE - offset;
+ if (this_len > len)
+ this_len = len;
+
+ buf->page = page;
+ buf->offset = offset;
+ buf->len = this_len;
+ buf->ops = &page_cache_pipe_buf_ops;
+ info->nrbufs = ++bufs;
+ do_wakeup = 1;
+
+ ret += this_len;
+ len -= this_len;
+ offset = 0;
+ if (!--nr_pages)
+ break;
+ if (!len)
+ break;
+ if (bufs < PIPE_BUFFERS)
+ continue;
+
+ break;
+ }
+
+ if (signal_pending(current)) {
+ if (!ret)
+ ret = -ERESTARTSYS;
+ break;
+ }
+
+ if (do_wakeup) {
+ wake_up_interruptible_sync(PIPE_WAIT(*inode));
+ kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO,
+ POLL_IN);
+ do_wakeup = 0;
+ }
+
+ PIPE_WAITING_WRITERS(*inode)++;
+ pipe_wait(inode);
+ PIPE_WAITING_WRITERS(*inode)--;
+ }
+
+ mutex_unlock(PIPE_MUTEX(*inode));
+
+ if (do_wakeup) {
+ wake_up_interruptible(PIPE_WAIT(*inode));
+ kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
+ }
+
+ while (i < nr_pages)
+ page_cache_release(pages[i++]);
+
+ return ret;
+}
+
+static int __generic_file_splice_read(struct file *in, struct inode *pipe,
+ size_t len)
+{
+ struct address_space *mapping = in->f_mapping;
+ unsigned int offset, nr_pages;
+ struct page *pages[PIPE_BUFFERS], *shadow[PIPE_BUFFERS];
+ struct page *page;
+ pgoff_t index, pidx;
+ int i, j;
+
+ index = in->f_pos >> PAGE_CACHE_SHIFT;
+ offset = in->f_pos & ~PAGE_CACHE_MASK;
+ nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+
+ if (nr_pages > PIPE_BUFFERS)
+ nr_pages = PIPE_BUFFERS;
+
+ /*
+ * initiate read-ahead on this page range
+ */
+ do_page_cache_readahead(mapping, in, index, nr_pages);
+
+ /*
+ * Get as many pages from the page cache as possible..
+ * Start IO on the page cache entries we create (we
+ * can assume that any pre-existing ones we find have
+ * already had IO started on them).
+ */
+ i = find_get_pages(mapping, index, nr_pages, pages);
+
+ /*
+ * common case - we found all pages and they are contiguous,
+ * kick them off
+ */
+ if (i && (pages[i - 1]->index == index + i - 1))
+ goto splice_them;
+
+ /*
+ * fill shadow[] with pages at the right locations, so we only
+ * have to fill holes
+ */
+ memset(shadow, 0, i * sizeof(struct page *));
+ for (j = 0, pidx = index; j < i; pidx++, j++)
+ shadow[pages[j]->index - pidx] = pages[j];
+
+ /*
+ * now fill in the holes
+ */
+ for (i = 0, pidx = index; i < nr_pages; pidx++, i++) {
+ int error;
+
+ if (shadow[i])
+ continue;
+
+ /*
+ * no page there, look one up / create it
+ */
+ page = find_or_create_page(mapping, pidx,
+ mapping_gfp_mask(mapping));
+ if (!page)
+ break;
+
+ if (PageUptodate(page))
+ unlock_page(page);
+ else {
+ error = mapping->a_ops->readpage(in, page);
+
+ if (unlikely(error)) {
+ page_cache_release(page);
+ break;
+ }
+ }
+ shadow[i] = page;
+ }
+
+ if (!i) {
+ for (i = 0; i < nr_pages; i++) {
+ if (shadow[i])
+ page_cache_release(shadow[i]);
+ }
+ return 0;
+ }
+
+ memcpy(pages, shadow, i * sizeof(struct page *));
+
+ /*
+ * Now we splice them into the pipe..
+ */
+splice_them:
+ return move_to_pipe(pipe, pages, i, offset, len);
+}
+
+ssize_t generic_file_splice_read(struct file *in, struct inode *pipe,
+ size_t len, unsigned int flags)
+{
+ ssize_t spliced;
+ int ret;
+
+ ret = 0;
+ spliced = 0;
+ while (len) {
+ ret = __generic_file_splice_read(in, pipe, len);
+
+ if (ret <= 0)
+ break;
+
+ in->f_pos += ret;
+ len -= ret;
+ spliced += ret;
+ }
+
+ if (spliced)
+ return spliced;
+
+ return ret;
+}
+
+/*
+ * Send 'len' bytes to socket from 'file' at position 'pos' using sendpage().
+ */
+static int pipe_to_sendpage(struct pipe_inode_info *info,
+ struct pipe_buffer *buf, struct splice_desc *sd)
+{
+ struct file *file = sd->file;
+ loff_t pos = sd->pos;
+ unsigned int offset;
+ ssize_t ret;
+ void *ptr;
+
+ /*
+ * sub-optimal, but we are limited by the pipe ->map. we don't
+ * need a kmap'ed buffer here, we just want to make sure we
+ * have the page pinned if the pipe page originates from the
+ * page cache
+ */
+ ptr = buf->ops->map(file, info, buf);
+ if (IS_ERR(ptr))
+ return PTR_ERR(ptr);
+
+ offset = pos & ~PAGE_CACHE_MASK;
+
+ ret = file->f_op->sendpage(file, buf->page, offset, sd->len, &pos,
+ sd->len < sd->total_len);
+
+ buf->ops->unmap(info, buf);
+ if (ret == sd->len)
+ return 0;
+
+ return -EIO;
+}
+
+/*
+ * This is a little more tricky than the file -> pipe splicing. There are
+ * basically three cases:
+ *
+ * - Destination page already exists in the address space and there
+ * are users of it. For that case we have no other option that
+ * copying the data. Tough luck.
+ * - Destination page already exists in the address space, but there
+ * are no users of it. Make sure it's uptodate, then drop it. Fall
+ * through to last case.
+ * - 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...
+ */
+static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
+ struct splice_desc *sd)
+{
+ struct file *file = sd->file;
+ struct address_space *mapping = file->f_mapping;
+ unsigned int offset;
+ struct page *page;
+ char *src, *dst;
+ pgoff_t index;
+ int ret;
+
+ /*
+ * after this, page will be locked and unmapped
+ */
+ src = buf->ops->map(file, info, buf);
+ if (IS_ERR(src))
+ return PTR_ERR(src);
+
+ index = sd->pos >> PAGE_CACHE_SHIFT;
+ offset = sd->pos & ~PAGE_CACHE_MASK;
+
+find_page:
+ ret = -ENOMEM;
+ page = find_or_create_page(mapping, index, mapping_gfp_mask(mapping));
+ if (!page)
+ goto out;
+
+ /*
+ * If the page is uptodate, it is also locked. If it isn't
+ * uptodate, we can mark it uptodate if we are filling the
+ * full page. Otherwise we need to read it in first...
+ */
+ if (!PageUptodate(page)) {
+ if (sd->len < PAGE_CACHE_SIZE) {
+ ret = mapping->a_ops->readpage(file, page);
+ if (unlikely(ret))
+ goto out;
+
+ lock_page(page);
+
+ if (!PageUptodate(page)) {
+ /*
+ * page got invalidated, repeat
+ */
+ if (!page->mapping) {
+ unlock_page(page);
+ page_cache_release(page);
+ goto find_page;
+ }
+ ret = -EIO;
+ goto out;
+ }
+ } else {
+ WARN_ON(!PageLocked(page));
+ SetPageUptodate(page);
+ }
+ }
+
+ ret = mapping->a_ops->prepare_write(file, page, 0, sd->len);
+ if (ret)
+ goto out;
+
+ dst = kmap_atomic(page, KM_USER0);
+ memcpy(dst + offset, src + buf->offset, sd->len);
+ flush_dcache_page(page);
+ kunmap_atomic(dst, KM_USER0);
+
+ ret = mapping->a_ops->commit_write(file, page, 0, sd->len);
+ if (ret < 0)
+ goto out;
+
+ set_page_dirty(page);
+ ret = write_one_page(page, 0);
+out:
+ if (ret < 0)
+ unlock_page(page);
+ page_cache_release(page);
+ buf->ops->unmap(info, buf);
+ return ret;
+}
+
+typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
+ struct splice_desc *);
+
+static ssize_t move_from_pipe(struct inode *inode, struct file *out,
+ size_t len, unsigned int flags,
+ splice_actor *actor)
+{
+ struct pipe_inode_info *info;
+ int ret, do_wakeup, err;
+ struct splice_desc sd;
+
+ ret = 0;
+ do_wakeup = 0;
+
+ sd.total_len = len;
+ sd.flags = flags;
+ sd.file = out;
+ sd.pos = out->f_pos;
+
+ mutex_lock(PIPE_MUTEX(*inode));
+
+ info = inode->i_pipe;
+ for (;;) {
+ int bufs = info->nrbufs;
+
+ if (bufs) {
+ int curbuf = info->curbuf;
+ struct pipe_buffer *buf = info->bufs + curbuf;
+ struct pipe_buf_operations *ops = buf->ops;
+
+ sd.len = buf->len;
+ if (sd.len > sd.total_len)
+ sd.len = sd.total_len;
+
+ err = actor(info, buf, &sd);
+ if (err) {
+ if (!ret && err != -ENODATA)
+ ret = err;
+
+ break;
+ }
+
+ ret += sd.len;
+ buf->offset += sd.len;
+ buf->len -= sd.len;
+ if (!buf->len) {
+ buf->ops = NULL;
+ ops->release(info, buf);
+ curbuf = (curbuf + 1) & (PIPE_BUFFERS - 1);
+ info->curbuf = curbuf;
+ info->nrbufs = --bufs;
+ do_wakeup = 1;
+ }
+
+ sd.pos += sd.len;
+ sd.total_len -= sd.len;
+ if (!sd.total_len)
+ break;
+ }
+
+ if (bufs)
+ continue;
+ if (!PIPE_WRITERS(*inode))
+ break;
+ if (!PIPE_WAITING_WRITERS(*inode)) {
+ if (ret)
+ break;
+ }
+
+ if (signal_pending(current)) {
+ if (!ret)
+ ret = -ERESTARTSYS;
+ break;
+ }
+
+ if (do_wakeup) {
+ wake_up_interruptible_sync(PIPE_WAIT(*inode));
+ kill_fasync(PIPE_FASYNC_WRITERS(*inode),SIGIO,POLL_OUT);
+ do_wakeup = 0;
+ }
+
+ pipe_wait(inode);
+ }
+
+ mutex_unlock(PIPE_MUTEX(*inode));
+
+ if (do_wakeup) {
+ wake_up_interruptible(PIPE_WAIT(*inode));
+ kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
+ }
+
+ mutex_lock(&out->f_mapping->host->i_mutex);
+ out->f_pos = sd.pos;
+ mutex_unlock(&out->f_mapping->host->i_mutex);
+ return ret;
+
+}
+
+ssize_t generic_file_splice_write(struct inode *inode, struct file *out,
+ size_t len, unsigned int flags)
+{
+ return move_from_pipe(inode, out, len, flags, pipe_to_file);
+}
+
+ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,
+ size_t len, unsigned int flags)
+{
+ return move_from_pipe(inode, out, len, flags, pipe_to_sendpage);
+}
+
+static long do_splice_from(struct inode *pipe, struct file *out, size_t len,
+ unsigned int flags)
+{
+ loff_t pos;
+ int ret;
+
+ if (!out->f_op || !out->f_op->splice_write)
+ return -EINVAL;
+
+ if (!(out->f_mode & FMODE_WRITE))
+ return -EBADF;
+
+ pos = out->f_pos;
+ ret = rw_verify_area(WRITE, out, &pos, len);
+ if (unlikely(ret < 0))
+ return ret;
+
+ return out->f_op->splice_write(pipe, out, len, flags);
+}
+
+static long do_splice_to(struct file *in, struct inode *pipe, size_t len,
+ unsigned int flags)
+{
+ loff_t pos, isize, left;
+ int ret;
+
+ if (!in->f_op || !in->f_op->splice_read)
+ return -EINVAL;
+
+ if (!(in->f_mode & FMODE_READ))
+ return -EBADF;
+
+ pos = in->f_pos;
+ ret = rw_verify_area(READ, in, &pos, len);
+ if (unlikely(ret < 0))
+ return ret;
+
+ isize = i_size_read(in->f_mapping->host);
+ if (unlikely(in->f_pos >= isize))
+ return 0;
+
+ left = isize - in->f_pos;
+ if (left < len)
+ len = left;
+
+ return in->f_op->splice_read(in, pipe, len, flags);
+}
+
+static long do_splice(struct file *in, struct file *out, size_t len,
+ unsigned int flags)
+{
+ struct inode *pipe;
+
+ pipe = in->f_dentry->d_inode;
+ if (pipe->i_pipe)
+ return do_splice_from(pipe, out, len, flags);
+
+ pipe = out->f_dentry->d_inode;
+ if (pipe->i_pipe)
+ return do_splice_to(in, pipe, len, flags);
+
+ return -EINVAL;
+}
+
+asmlinkage long sys_splice(int fdin, int fdout, size_t len, unsigned int flags)
+{
+ long error;
+ struct file *in, *out;
+ int fput_in, fput_out;
+
+ if (unlikely(!len))
+ return 0;
+
+ error = -EBADF;
+ in = fget_light(fdin, &fput_in);
+ if (in) {
+ if (in->f_mode & FMODE_READ) {
+ out = fget_light(fdout, &fput_out);
+ if (out) {
+ if (out->f_mode & FMODE_WRITE)
+ error = do_splice(in, out, len, flags);
+ fput_light(out, fput_out);
+ }
+ }
+
+ fput_light(in, fput_in);
+ }
+
+ return error;
+}