linux/fs/splice.c

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21 KiB
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/*
* "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>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h>
#include <linux/module.h>
#include <linux/syscalls.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 */
};
/*
* 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)
{
struct page *page = buf->page;
struct address_space *mapping = page_mapping(page);
WARN_ON(!PageLocked(page));
WARN_ON(!PageUptodate(page));
/*
* At least for ext2 with nobh option, we need to wait on writeback
* completing on this page, since we'll remove it from the pagecache.
* Otherwise truncate wont wait on the page, allowing the disk
* blocks to be reused by someone else before we actually wrote our
* data to them. fs corruption ensues.
*/
wait_on_page_writeback(page);
if (PagePrivate(page))
try_to_release_page(page, mapping_gfp_mask(mapping));
if (!remove_mapping(mapping, page))
return 1;
buf->flags |= PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU;
return 0;
}
static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
page_cache_release(buf->page);
buf->page = NULL;
buf->flags &= ~(PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU);
}
static void *page_cache_pipe_buf_map(struct file *file,
struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
struct page *page = buf->page;
int err;
if (!PageUptodate(page)) {
lock_page(page);
/*
* Page got truncated/unhashed. This will cause a 0-byte
* splice, if this is the first page
*/
if (!page->mapping) {
err = -ENODATA;
goto error;
}
/*
* uh oh, read-error from disk
*/
if (!PageUptodate(page)) {
err = -EIO;
goto error;
}
/*
* page is ok afterall, fall through to mapping
*/
unlock_page(page);
}
return kmap(page);
error:
unlock_page(page);
return ERR_PTR(err);
}
static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
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,
.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 pipe_inode_info *pipe, struct page **pages,
int nr_pages, unsigned long offset,
unsigned long len, unsigned int flags)
{
int ret, do_wakeup, i;
ret = 0;
do_wakeup = 0;
i = 0;
if (pipe->inode)
mutex_lock(&pipe->inode->i_mutex);
for (;;) {
if (!pipe->readers) {
send_sig(SIGPIPE, current, 0);
if (!ret)
ret = -EPIPE;
break;
}
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;
pipe->nrbufs++;
if (pipe->inode)
do_wakeup = 1;
ret += this_len;
len -= this_len;
offset = 0;
if (!--nr_pages)
break;
if (!len)
break;
if (pipe->nrbufs < PIPE_BUFFERS)
continue;
break;
}
if (flags & SPLICE_F_NONBLOCK) {
if (!ret)
ret = -EAGAIN;
break;
}
if (signal_pending(current)) {
if (!ret)
ret = -ERESTARTSYS;
break;
}
if (do_wakeup) {
smp_mb();
if (waitqueue_active(&pipe->wait))
wake_up_interruptible_sync(&pipe->wait);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
do_wakeup = 0;
}
pipe->waiting_writers++;
pipe_wait(pipe);
pipe->waiting_writers--;
}
if (pipe->inode)
mutex_unlock(&pipe->inode->i_mutex);
if (do_wakeup) {
smp_mb();
if (waitqueue_active(&pipe->wait))
wake_up_interruptible(&pipe->wait);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
}
while (i < nr_pages)
page_cache_release(pages[i++]);
return ret;
}
static int
__generic_file_splice_read(struct file *in, struct pipe_inode_info *pipe,
size_t len, unsigned int flags)
{
struct address_space *mapping = in->f_mapping;
unsigned int offset, nr_pages;
struct page *pages[PIPE_BUFFERS];
struct page *page;
pgoff_t index;
int i, error;
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. however, don't call into
* 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);
/*
* now fill in the holes
*/
error = 0;
for (i = 0; i < nr_pages; i++, index++) {
find_page:
/*
* lookup the page for this index
*/
page = find_get_page(mapping, index);
if (!page) {
/*
* If in nonblock mode then dont block on
* readpage (we've kicked readahead so there
* will be asynchronous progress):
*/
if (flags & SPLICE_F_NONBLOCK)
break;
/*
* page didn't exist, allocate one
*/
page = page_cache_alloc_cold(mapping);
if (!page)
break;
error = add_to_page_cache_lru(page, mapping, index,
mapping_gfp_mask(mapping));
if (unlikely(error)) {
page_cache_release(page);
break;
}
goto readpage;
}
/*
* If the page isn't uptodate, we may need to start io on it
*/
if (!PageUptodate(page)) {
lock_page(page);
/*
* page was truncated, stop here. if this isn't the
* first page, we'll just complete what we already
* added
*/
if (!page->mapping) {
unlock_page(page);
page_cache_release(page);
break;
}
/*
* page was already under io and is now done, great
*/
if (PageUptodate(page)) {
unlock_page(page);
goto fill_it;
}
readpage:
/*
* need to read in the page
*/
error = mapping->a_ops->readpage(in, page);
if (unlikely(error)) {
page_cache_release(page);
if (error == AOP_TRUNCATED_PAGE)
goto find_page;
break;
}
}
fill_it:
pages[i] = page;
}
if (i)
return move_to_pipe(pipe, pages, i, offset, len, flags);
return error;
}
/**
* 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 pipe_inode_info *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, flags);
if (ret <= 0)
break;
in->f_pos += ret;
len -= ret;
spliced += ret;
if (!(flags & SPLICE_F_NONBLOCK))
continue;
ret = -EAGAIN;
break;
}
if (spliced)
return spliced;
return ret;
}
EXPORT_SYMBOL(generic_file_splice_read);
/*
* Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->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;
int more;
/*
* 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;
more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
ret = file->f_op->sendpage(file, buf->page, offset, sd->len, &pos,more);
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.
*
* 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)
{
struct file *file = sd->file;
struct address_space *mapping = file->f_mapping;
gfp_t gfp_mask = mapping_gfp_mask(mapping);
unsigned int offset;
struct page *page;
pgoff_t index;
char *src;
int ret;
/*
* make sure the data in this buffer is uptodate
*/
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;
/*
* 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;
/*
* this will also set the page locked
*/
page = buf->page;
if (add_to_page_cache(page, mapping, index, gfp_mask))
goto find_page;
if (!(buf->flags & PIPE_BUF_FLAG_LRU))
lru_cache_add(page);
} else {
find_page:
ret = -ENOMEM;
page = find_or_create_page(mapping, index, gfp_mask);
if (!page)
goto out_nomem;
/*
* 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 == AOP_TRUNCATED_PAGE) {
page_cache_release(page);
goto find_page;
} else if (ret)
goto out;
if (!(buf->flags & PIPE_BUF_FLAG_STOLEN)) {
char *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 == AOP_TRUNCATED_PAGE) {
page_cache_release(page);
goto find_page;
} else if (ret)
goto out;
mark_page_accessed(page);
balance_dirty_pages_ratelimited(mapping);
out:
if (!(buf->flags & PIPE_BUF_FLAG_STOLEN)) {
page_cache_release(page);
unlock_page(page);
}
out_nomem:
buf->ops->unmap(info, buf);
return ret;
}
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 pipe_inode_info *pipe, struct file *out,
size_t len, unsigned int flags,
splice_actor *actor)
{
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;
if (pipe->inode)
mutex_lock(&pipe->inode->i_mutex);
for (;;) {
if (pipe->nrbufs) {
struct pipe_buffer *buf = pipe->bufs + pipe->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(pipe, 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(pipe, buf);
pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
pipe->nrbufs--;
if (pipe->inode)
do_wakeup = 1;
}
sd.pos += sd.len;
sd.total_len -= sd.len;
if (!sd.total_len)
break;
}
if (pipe->nrbufs)
continue;
if (!pipe->writers)
break;
if (!pipe->waiting_writers) {
if (ret)
break;
}
if (flags & SPLICE_F_NONBLOCK) {
if (!ret)
ret = -EAGAIN;
break;
}
if (signal_pending(current)) {
if (!ret)
ret = -ERESTARTSYS;
break;
}
if (do_wakeup) {
smp_mb();
if (waitqueue_active(&pipe->wait))
wake_up_interruptible_sync(&pipe->wait);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
do_wakeup = 0;
}
pipe_wait(pipe);
}
if (pipe->inode)
mutex_unlock(&pipe->inode->i_mutex);
if (do_wakeup) {
smp_mb();
if (waitqueue_active(&pipe->wait))
wake_up_interruptible(&pipe->wait);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
}
out->f_pos = sd.pos;
return ret;
}
/**
* generic_file_splice_write - splice data from a pipe to a file
* @pipe: pipe info
* @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 pipe_inode_info *pipe, struct file *out,
size_t len, unsigned int flags)
{
struct address_space *mapping = out->f_mapping;
ssize_t ret;
ret = move_from_pipe(pipe, out, len, flags, pipe_to_file);
/*
* if file or inode is SYNC and we actually wrote some data, sync it
*/
if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(mapping->host))
&& ret > 0) {
struct inode *inode = mapping->host;
int err;
mutex_lock(&inode->i_mutex);
err = generic_osync_inode(mapping->host, mapping,
OSYNC_METADATA|OSYNC_DATA);
mutex_unlock(&inode->i_mutex);
if (err)
ret = err;
}
return ret;
}
EXPORT_SYMBOL(generic_file_splice_write);
/**
* 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 pipe_inode_info *pipe, struct file *out,
size_t len, unsigned int flags)
{
return move_from_pipe(pipe, out, len, flags, pipe_to_sendpage);
}
EXPORT_SYMBOL(generic_splice_sendpage);
/*
* Attempt to initiate a splice from pipe to file.
*/
static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
size_t len, unsigned int flags)
{
loff_t pos;
int ret;
if (unlikely(!out->f_op || !out->f_op->splice_write))
return -EINVAL;
if (unlikely(!(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);
}
/*
* Attempt to initiate a splice from a file to a pipe.
*/
static long do_splice_to(struct file *in, struct pipe_inode_info *pipe,
size_t len, unsigned int flags)
{
loff_t pos, isize, left;
int ret;
if (unlikely(!in->f_op || !in->f_op->splice_read))
return -EINVAL;
if (unlikely(!(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 (unlikely(left < len))
len = left;
return in->f_op->splice_read(in, pipe, len, flags);
}
long do_splice_direct(struct file *in, struct file *out, size_t len,
unsigned int flags)
{
struct pipe_inode_info *pipe;
long ret, bytes;
umode_t i_mode;
int i;
/*
* We require the input being a regular file, as we don't want to
* randomly drop data for eg socket -> socket splicing. Use the
* piped splicing for that!
*/
i_mode = in->f_dentry->d_inode->i_mode;
if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
return -EINVAL;
/*
* neither in nor out is a pipe, setup an internal pipe attached to
* 'out' and transfer the wanted data from 'in' to 'out' through that
*/
pipe = current->splice_pipe;
if (unlikely(!pipe)) {
pipe = alloc_pipe_info(NULL);
if (!pipe)
return -ENOMEM;
/*
* We don't have an immediate reader, but we'll read the stuff
* out of the pipe right after the move_to_pipe(). So set
* PIPE_READERS appropriately.
*/
pipe->readers = 1;
current->splice_pipe = pipe;
}
/*
* do the splice
*/
ret = 0;
bytes = 0;
while (len) {
size_t read_len, max_read_len;
/*
* Do at most PIPE_BUFFERS pages worth of transfer:
*/
max_read_len = min(len, (size_t)(PIPE_BUFFERS*PAGE_SIZE));
ret = do_splice_to(in, pipe, max_read_len, flags);
if (unlikely(ret < 0))
goto out_release;
read_len = ret;
/*
* NOTE: nonblocking mode only applies to the input. We
* must not do the output in nonblocking mode as then we
* could get stuck data in the internal pipe:
*/
ret = do_splice_from(pipe, out, read_len,
flags & ~SPLICE_F_NONBLOCK);
if (unlikely(ret < 0))
goto out_release;
bytes += ret;
len -= ret;
/*
* In nonblocking mode, if we got back a short read then
* that was due to either an IO error or due to the
* pagecache entry not being there. In the IO error case
* the _next_ splice attempt will produce a clean IO error
* return value (not a short read), so in both cases it's
* correct to break out of the loop here:
*/
if ((flags & SPLICE_F_NONBLOCK) && (read_len < max_read_len))
break;
}
pipe->nrbufs = pipe->curbuf = 0;
return bytes;
out_release:
/*
* If we did an incomplete transfer we must release
* the pipe buffers in question:
*/
for (i = 0; i < PIPE_BUFFERS; i++) {
struct pipe_buffer *buf = pipe->bufs + i;
if (buf->ops) {
buf->ops->release(pipe, buf);
buf->ops = NULL;
}
}
pipe->nrbufs = pipe->curbuf = 0;
/*
* If we transferred some data, return the number of bytes:
*/
if (bytes > 0)
return bytes;
return ret;
}
EXPORT_SYMBOL(do_splice_direct);
/*
* Determine where to splice to/from.
*/
static long do_splice(struct file *in, loff_t __user *off_in,
struct file *out, loff_t __user *off_out,
size_t len, unsigned int flags)
{
struct pipe_inode_info *pipe;
pipe = in->f_dentry->d_inode->i_pipe;
if (pipe) {
if (off_in)
return -ESPIPE;
if (off_out) {
if (out->f_op->llseek == no_llseek)
return -EINVAL;
if (copy_from_user(&out->f_pos, off_out,
sizeof(loff_t)))
return -EFAULT;
}
return do_splice_from(pipe, out, len, flags);
}
pipe = out->f_dentry->d_inode->i_pipe;
if (pipe) {
if (off_out)
return -ESPIPE;
if (off_in) {
if (in->f_op->llseek == no_llseek)
return -EINVAL;
if (copy_from_user(&in->f_pos, off_in, sizeof(loff_t)))
return -EFAULT;
}
return do_splice_to(in, pipe, len, flags);
}
return -EINVAL;
}
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)
{
long error;
struct file *in, *out;
int fput_in, fput_out;
if (unlikely(!len))
return 0;
error = -EBADF;
in = fget_light(fd_in, &fput_in);
if (in) {
if (in->f_mode & FMODE_READ) {
out = fget_light(fd_out, &fput_out);
if (out) {
if (out->f_mode & FMODE_WRITE)
error = do_splice(in, off_in,
out, off_out,
len, flags);
fput_light(out, fput_out);
}
}
fput_light(in, fput_in);
}
return error;
}