[PATCH] Add support for the sys_vmsplice syscall
sys_splice() moves data to/from pipes with a file input/output. sys_vmsplice()
moves data to a pipe, with the input being a user address range instead.
This uses an approach suggested by Linus, where we can hold partial ranges
inside the pages[] map. Hopefully this will be useful for network
receive support as well.
Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/fs/splice.c b/fs/splice.c
index 8c6030c..0b2c1f0 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -27,6 +27,7 @@
#include <linux/buffer_head.h>
#include <linux/module.h>
#include <linux/syscalls.h>
+#include <linux/uio.h>
/*
* Passed to the actors
@@ -38,6 +39,22 @@
loff_t pos; /* file position */
};
+struct partial_page {
+ unsigned int offset;
+ unsigned int len;
+};
+
+/*
+ * Passed to move_to_pipe
+ */
+struct splice_pipe_desc {
+ struct page **pages; /* page map */
+ struct partial_page *partial; /* pages[] may not be contig */
+ int nr_pages; /* number of pages in map */
+ unsigned int flags; /* splice flags */
+ struct pipe_buf_operations *ops;/* ops associated with output pipe */
+};
+
/*
* 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
@@ -128,6 +145,19 @@
kunmap(buf->page);
}
+static void *user_page_pipe_buf_map(struct file *file,
+ struct pipe_inode_info *pipe,
+ struct pipe_buffer *buf)
+{
+ return kmap(buf->page);
+}
+
+static void user_page_pipe_buf_unmap(struct pipe_inode_info *pipe,
+ struct pipe_buffer *buf)
+{
+ kunmap(buf->page);
+}
+
static void page_cache_pipe_buf_get(struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
@@ -143,19 +173,33 @@
.get = page_cache_pipe_buf_get,
};
+static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
+ struct pipe_buffer *buf)
+{
+ return 1;
+}
+
+static struct pipe_buf_operations user_page_pipe_buf_ops = {
+ .can_merge = 0,
+ .map = user_page_pipe_buf_map,
+ .unmap = user_page_pipe_buf_unmap,
+ .release = page_cache_pipe_buf_release,
+ .steal = user_page_pipe_buf_steal,
+ .get = page_cache_pipe_buf_get,
+};
+
/*
* 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 pipe_inode_info *pipe, struct page **pages,
- int nr_pages, unsigned long len,
- unsigned int offset, unsigned int flags)
+static ssize_t move_to_pipe(struct pipe_inode_info *pipe,
+ struct splice_pipe_desc *spd)
{
- int ret, do_wakeup, i;
+ int ret, do_wakeup, page_nr;
ret = 0;
do_wakeup = 0;
- i = 0;
+ page_nr = 0;
if (pipe->inode)
mutex_lock(&pipe->inode->i_mutex);
@@ -171,27 +215,19 @@
if (pipe->nrbufs < PIPE_BUFFERS) {
int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
struct pipe_buffer *buf = pipe->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;
+ buf->page = spd->pages[page_nr];
+ buf->offset = spd->partial[page_nr].offset;
+ buf->len = spd->partial[page_nr].len;
+ buf->ops = spd->ops;
pipe->nrbufs++;
+ page_nr++;
+ ret += buf->len;
+
if (pipe->inode)
do_wakeup = 1;
- ret += this_len;
- len -= this_len;
- offset = 0;
- if (!--nr_pages)
- break;
- if (!len)
+ if (!--spd->nr_pages)
break;
if (pipe->nrbufs < PIPE_BUFFERS)
continue;
@@ -199,7 +235,7 @@
break;
}
- if (flags & SPLICE_F_NONBLOCK) {
+ if (spd->flags & SPLICE_F_NONBLOCK) {
if (!ret)
ret = -EAGAIN;
break;
@@ -234,8 +270,8 @@
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
}
- while (i < nr_pages)
- page_cache_release(pages[i++]);
+ while (page_nr < spd->nr_pages)
+ page_cache_release(spd->pages[page_nr++]);
return ret;
}
@@ -246,17 +282,24 @@
unsigned int flags)
{
struct address_space *mapping = in->f_mapping;
- unsigned int loff, offset, nr_pages;
+ unsigned int loff, nr_pages;
struct page *pages[PIPE_BUFFERS];
+ struct partial_page partial[PIPE_BUFFERS];
struct page *page;
pgoff_t index, end_index;
loff_t isize;
- size_t bytes;
- int i, error;
+ size_t total_len;
+ int error;
+ struct splice_pipe_desc spd = {
+ .pages = pages,
+ .partial = partial,
+ .flags = flags,
+ .ops = &page_cache_pipe_buf_ops,
+ };
index = *ppos >> PAGE_CACHE_SHIFT;
- loff = offset = *ppos & ~PAGE_CACHE_MASK;
- nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+ loff = *ppos & ~PAGE_CACHE_MASK;
+ nr_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
if (nr_pages > PIPE_BUFFERS)
nr_pages = PIPE_BUFFERS;
@@ -266,15 +309,15 @@
* read-ahead if this is a non-zero offset (we are likely doing small
* chunk splice and the page is already there) for a single page.
*/
- if (!offset || nr_pages > 1)
- do_page_cache_readahead(mapping, in, index, nr_pages);
+ if (!loff || spd.nr_pages > 1)
+ do_page_cache_readahead(mapping, in, index, spd.nr_pages);
/*
* Now fill in the holes:
*/
error = 0;
- bytes = 0;
- for (i = 0; i < nr_pages; i++, index++) {
+ total_len = 0;
+ for (spd.nr_pages = 0; spd.nr_pages < nr_pages; spd.nr_pages++, index++) {
unsigned int this_len;
if (!len)
@@ -367,26 +410,29 @@
*/
if (end_index == index) {
loff = PAGE_CACHE_SIZE - (isize & ~PAGE_CACHE_MASK);
- if (bytes + loff > isize) {
+ if (total_len + loff > isize) {
page_cache_release(page);
break;
}
/*
* force quit after adding this page
*/
- nr_pages = i;
+ nr_pages = spd.nr_pages;
this_len = min(this_len, loff);
+ loff = 0;
}
}
fill_it:
- pages[i] = page;
- bytes += this_len;
+ pages[spd.nr_pages] = page;
+ partial[spd.nr_pages].offset = loff;
+ partial[spd.nr_pages].len = this_len;
len -= this_len;
+ total_len += this_len;
loff = 0;
}
- if (i)
- return move_to_pipe(pipe, pages, i, bytes, offset, flags);
+ if (spd.nr_pages)
+ return move_to_pipe(pipe, &spd);
return error;
}
@@ -1018,6 +1064,174 @@
return -EINVAL;
}
+/*
+ * Map an iov into an array of pages and offset/length tupples. With the
+ * partial_page structure, we can map several non-contiguous ranges into
+ * our ones pages[] map instead of splitting that operation into pieces.
+ * Could easily be exported as a generic helper for other users, in which
+ * case one would probably want to add a 'max_nr_pages' parameter as well.
+ */
+static int get_iovec_page_array(const struct iovec __user *iov,
+ unsigned int nr_vecs, struct page **pages,
+ struct partial_page *partial)
+{
+ int buffers = 0, error = 0;
+
+ /*
+ * It's ok to take the mmap_sem for reading, even
+ * across a "get_user()".
+ */
+ down_read(¤t->mm->mmap_sem);
+
+ while (nr_vecs) {
+ unsigned long off, npages;
+ void __user *base;
+ size_t len;
+ int i;
+
+ /*
+ * Get user address base and length for this iovec.
+ */
+ error = get_user(base, &iov->iov_base);
+ if (unlikely(error))
+ break;
+ error = get_user(len, &iov->iov_len);
+ if (unlikely(error))
+ break;
+
+ /*
+ * Sanity check this iovec. 0 read succeeds.
+ */
+ if (unlikely(!len))
+ break;
+ error = -EFAULT;
+ if (unlikely(!base))
+ break;
+
+ /*
+ * Get this base offset and number of pages, then map
+ * in the user pages.
+ */
+ off = (unsigned long) base & ~PAGE_MASK;
+ npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ if (npages > PIPE_BUFFERS - buffers)
+ npages = PIPE_BUFFERS - buffers;
+
+ error = get_user_pages(current, current->mm,
+ (unsigned long) base, npages, 0, 0,
+ &pages[buffers], NULL);
+
+ if (unlikely(error <= 0))
+ break;
+
+ /*
+ * Fill this contiguous range into the partial page map.
+ */
+ for (i = 0; i < error; i++) {
+ const int plen = min_t(size_t, len, PAGE_SIZE) - off;
+
+ partial[buffers].offset = off;
+ partial[buffers].len = plen;
+
+ off = 0;
+ len -= plen;
+ buffers++;
+ }
+
+ /*
+ * We didn't complete this iov, stop here since it probably
+ * means we have to move some of this into a pipe to
+ * be able to continue.
+ */
+ if (len)
+ break;
+
+ /*
+ * Don't continue if we mapped fewer pages than we asked for,
+ * or if we mapped the max number of pages that we have
+ * room for.
+ */
+ if (error < npages || buffers == PIPE_BUFFERS)
+ break;
+
+ nr_vecs--;
+ iov++;
+ }
+
+ up_read(¤t->mm->mmap_sem);
+
+ if (buffers)
+ return buffers;
+
+ return error;
+}
+
+/*
+ * vmsplice splices a user address range into a pipe. It can be thought of
+ * as splice-from-memory, where the regular splice is splice-from-file (or
+ * to file). In both cases the output is a pipe, naturally.
+ *
+ * Note that vmsplice only supports splicing _from_ user memory to a pipe,
+ * not the other way around. Splicing from user memory is a simple operation
+ * that can be supported without any funky alignment restrictions or nasty
+ * vm tricks. We simply map in the user memory and fill them into a pipe.
+ * The reverse isn't quite as easy, though. There are two possible solutions
+ * for that:
+ *
+ * - memcpy() the data internally, at which point we might as well just
+ * do a regular read() on the buffer anyway.
+ * - Lots of nasty vm tricks, that are neither fast nor flexible (it
+ * has restriction limitations on both ends of the pipe).
+ *
+ * Alas, it isn't here.
+ *
+ */
+static long do_vmsplice(struct file *file, const struct iovec __user *iov,
+ unsigned long nr_segs, unsigned int flags)
+{
+ struct pipe_inode_info *pipe = file->f_dentry->d_inode->i_pipe;
+ struct page *pages[PIPE_BUFFERS];
+ struct partial_page partial[PIPE_BUFFERS];
+ struct splice_pipe_desc spd = {
+ .pages = pages,
+ .partial = partial,
+ .flags = flags,
+ .ops = &user_page_pipe_buf_ops,
+ };
+
+ if (unlikely(!pipe))
+ return -EBADF;
+ if (unlikely(nr_segs > UIO_MAXIOV))
+ return -EINVAL;
+ else if (unlikely(!nr_segs))
+ return 0;
+
+ spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial);
+ if (spd.nr_pages <= 0)
+ return spd.nr_pages;
+
+ return move_to_pipe(pipe, &spd);
+}
+
+asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
+ unsigned long nr_segs, unsigned int flags)
+{
+ struct file *file;
+ long error;
+ int fput;
+
+ error = -EBADF;
+ file = fget_light(fd, &fput);
+ if (file) {
+ if (file->f_mode & FMODE_WRITE)
+ error = do_vmsplice(file, iov, nr_segs, flags);
+
+ fput_light(file, fput);
+ }
+
+ return error;
+}
+
asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
int fd_out, loff_t __user *off_out,
size_t len, unsigned int flags)