[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>

1 files changed, 612 insertions, 0 deletions

diff --git a/fs/splice.c b/fs/splice.c
new file mode 100644
index 000000000000..efa47c1c4e13
--- /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;
+}