linux/fs/splice.c
Jeff Garzik a0f0678025 [PATCH] splice exports
Woe be unto he who builds their filesystems as modules.

Signed-off-by: Jeff Garzik <jeff@garzik.org>
[ Obscure quote from the infamous geek bible? ]
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-30 22:16:24 -08:00

664 lines
14 KiB
C

/*
* "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/module.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 int page_cache_pipe_buf_steal(struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
struct page *page = buf->page;
WARN_ON(!PageLocked(page));
WARN_ON(!PageUptodate(page));
if (!remove_mapping(page_mapping(page), page))
return 1;
if (PageLRU(page)) {
struct zone *zone = page_zone(page);
spin_lock_irq(&zone->lru_lock);
BUG_ON(!PageLRU(page));
__ClearPageLRU(page);
del_page_from_lru(zone, page);
spin_unlock_irq(&zone->lru_lock);
}
buf->stolen = 1;
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->stolen = 0;
}
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)
{
if (!buf->stolen)
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,
.steal = page_cache_pipe_buf_steal,
};
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;
pgoff_t index;
char *src;
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;
/*
* reuse buf page, if SPLICE_F_MOVE is set
*/
if (sd->flags & SPLICE_F_MOVE) {
if (buf->ops->steal(info, buf))
goto find_page;
page = buf->page;
if (add_to_page_cache_lru(page, mapping, index,
mapping_gfp_mask(mapping)))
goto find_page;
} else {
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;
if (!buf->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 < 0)
goto out;
set_page_dirty(page);
ret = write_one_page(page, 0);
out:
if (ret < 0)
unlock_page(page);
if (!buf->stolen)
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);
}
EXPORT_SYMBOL(generic_file_splice_write);
EXPORT_SYMBOL(generic_file_splice_read);
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;
}