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Subject[RFC PATCH] fuse: support splice() reading from fuse device
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This continues zero copy I/O support on the fuse interface.  The first
part of the patchset (splice write support on fuse device) was posted
here:

http://lkml.org/lkml/2010/4/28/215

With Jens' pipe growing patch and additional fuse patches it was
possible to achieve a 20GBytes/s write throghput on my laptop in a
"null" filesystem (no page cache, data goes to /dev/null).

Thanks,
Miklos

----
From: Miklos Szeredi <mszeredi@suse.cz>
Allow userspace filesystem implementation to use splice() to read from
the fuse device.

The filesystem can now transfer data coming from a WRITE request to an
arbitrary file descriptor (regular file, block device or socket)
without having to go through a userspace buffer.

The semantics of using splice() to read messages are:

1) with a single splice() move the whole message from the fuse
device to a temporary pipe
2) read the header from the pipe and determine the message type
3a) if message is a WRITE then splice data from pipe to destination
3b) else read the rest of the message

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
fs/fuse/dev.c | 223 +++++++++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 182 insertions(+), 41 deletions(-)
Index: linux-2.6/fs/fuse/dev.c
===================================================================
--- linux-2.6.orig/fs/fuse/dev.c 2010-05-13 10:54:19.000000000 +0200
+++ linux-2.6/fs/fuse/dev.c 2010-05-13 18:01:45.000000000 +0200
@@ -515,13 +515,12 @@ struct fuse_copy_state {
};

static void fuse_copy_init(struct fuse_copy_state *cs, struct fuse_conn *fc,
- int write, struct fuse_req *req,
+ int write,
const struct iovec *iov, unsigned long nr_segs)
{
memset(cs, 0, sizeof(*cs));
cs->fc = fc;
cs->write = write;
- cs->req = req;
cs->iov = iov;
cs->nr_segs = nr_segs;
}
@@ -532,8 +531,12 @@ static void fuse_copy_finish(struct fuse
if (cs->currbuf) {
struct pipe_buffer *buf = cs->currbuf;

- buf->ops->unmap(cs->pipe, buf, cs->mapaddr);
-
+ if (!cs->write) {
+ buf->ops->unmap(cs->pipe, buf, cs->mapaddr);
+ } else {
+ kunmap_atomic(cs->mapaddr, KM_USER0);
+ buf->len = PAGE_SIZE - cs->len;
+ }
cs->currbuf = NULL;
cs->mapaddr = NULL;
} else if (cs->mapaddr) {
@@ -561,17 +564,39 @@ static int fuse_copy_fill(struct fuse_co
if (cs->pipebufs) {
struct pipe_buffer *buf = cs->pipebufs;

- err = buf->ops->confirm(cs->pipe, buf);
- if (err)
- return err;
+ if (!cs->write) {
+ err = buf->ops->confirm(cs->pipe, buf);
+ if (err)
+ return err;
+
+ BUG_ON(!cs->nr_segs);
+ cs->currbuf = buf;
+ cs->mapaddr = buf->ops->map(cs->pipe, buf, 1);
+ cs->len = buf->len;
+ cs->buf = cs->mapaddr + buf->offset;
+ cs->pipebufs++;
+ cs->nr_segs--;
+ } else {
+ struct page *page;
+
+ if (cs->nr_segs == PIPE_BUFFERS)
+ return -EIO;

- BUG_ON(!cs->nr_segs);
- cs->currbuf = buf;
- cs->mapaddr = buf->ops->map(cs->pipe, buf, 1);
- cs->len = buf->len;
- cs->buf = cs->mapaddr + buf->offset;
- cs->pipebufs++;
- cs->nr_segs--;
+ page = alloc_page(GFP_HIGHUSER);
+ if (!page)
+ return -ENOMEM;
+
+ buf->page = page;
+ buf->offset = 0;
+ buf->len = 0;
+
+ cs->currbuf = buf;
+ cs->mapaddr = kmap_atomic(page, KM_USER0);
+ cs->buf = cs->mapaddr;
+ cs->len = PAGE_SIZE;
+ cs->pipebufs++;
+ cs->nr_segs++;
+ }
} else {
if (!cs->seglen) {
BUG_ON(!cs->nr_segs);
@@ -731,6 +756,30 @@ out_fallback:
return 1;
}

+static int fuse_ref_page(struct fuse_copy_state *cs, struct page *page,
+ unsigned offset, unsigned count)
+{
+ struct pipe_buffer *buf;
+
+ if (cs->nr_segs == PIPE_BUFFERS)
+ return -EIO;
+
+ unlock_request(cs->fc, cs->req);
+ fuse_copy_finish(cs);
+
+ buf = cs->pipebufs;
+ page_cache_get(page);
+ buf->page = page;
+ buf->offset = offset;
+ buf->len = count;
+
+ cs->pipebufs++;
+ cs->nr_segs++;
+ cs->len = 0;
+
+ return 0;
+}
+
/*
* Copy a page in the request to/from the userspace buffer. Must be
* done atomically
@@ -747,7 +796,9 @@ static int fuse_copy_page(struct fuse_co
kunmap_atomic(mapaddr, KM_USER1);
}
while (count) {
- if (!cs->len) {
+ if (cs->write && cs->pipebufs && page) {
+ return fuse_ref_page(cs, page, offset, count);
+ } else if (!cs->len) {
if (cs->move_pages && page &&
offset == 0 && count == PAGE_SIZE) {
err = fuse_try_move_page(cs, pagep);
@@ -862,11 +913,10 @@ __acquires(&fc->lock)
*
* Called with fc->lock held, releases it
*/
-static int fuse_read_interrupt(struct fuse_conn *fc, struct fuse_req *req,
- const struct iovec *iov, unsigned long nr_segs)
+static int fuse_read_interrupt(struct fuse_conn *fc, struct fuse_copy_state *cs,
+ size_t nbytes, struct fuse_req *req)
__releases(&fc->lock)
{
- struct fuse_copy_state cs;
struct fuse_in_header ih;
struct fuse_interrupt_in arg;
unsigned reqsize = sizeof(ih) + sizeof(arg);
@@ -882,14 +932,13 @@ __releases(&fc->lock)
arg.unique = req->in.h.unique;

spin_unlock(&fc->lock);
- if (iov_length(iov, nr_segs) < reqsize)
+ if (nbytes < reqsize)
return -EINVAL;

- fuse_copy_init(&cs, fc, 1, NULL, iov, nr_segs);
- err = fuse_copy_one(&cs, &ih, sizeof(ih));
+ err = fuse_copy_one(cs, &ih, sizeof(ih));
if (!err)
- err = fuse_copy_one(&cs, &arg, sizeof(arg));
- fuse_copy_finish(&cs);
+ err = fuse_copy_one(cs, &arg, sizeof(arg));
+ fuse_copy_finish(cs);

return err ? err : reqsize;
}
@@ -903,18 +952,13 @@ __releases(&fc->lock)
* request_end(). Otherwise add it to the processing list, and set
* the 'sent' flag.
*/
-static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
- unsigned long nr_segs, loff_t pos)
+static ssize_t fuse_dev_do_read(struct fuse_conn *fc, struct file *file,
+ struct fuse_copy_state *cs, size_t nbytes)
{
int err;
struct fuse_req *req;
struct fuse_in *in;
- struct fuse_copy_state cs;
unsigned reqsize;
- struct file *file = iocb->ki_filp;
- struct fuse_conn *fc = fuse_get_conn(file);
- if (!fc)
- return -EPERM;

restart:
spin_lock(&fc->lock);
@@ -934,7 +978,7 @@ static ssize_t fuse_dev_read(struct kioc
if (!list_empty(&fc->interrupts)) {
req = list_entry(fc->interrupts.next, struct fuse_req,
intr_entry);
- return fuse_read_interrupt(fc, req, iov, nr_segs);
+ return fuse_read_interrupt(fc, cs, nbytes, req);
}

req = list_entry(fc->pending.next, struct fuse_req, list);
@@ -944,7 +988,7 @@ static ssize_t fuse_dev_read(struct kioc
in = &req->in;
reqsize = in->h.len;
/* If request is too large, reply with an error and restart the read */
- if (iov_length(iov, nr_segs) < reqsize) {
+ if (nbytes < reqsize) {
req->out.h.error = -EIO;
/* SETXATTR is special, since it may contain too large data */
if (in->h.opcode == FUSE_SETXATTR)
@@ -953,12 +997,12 @@ static ssize_t fuse_dev_read(struct kioc
goto restart;
}
spin_unlock(&fc->lock);
- fuse_copy_init(&cs, fc, 1, req, iov, nr_segs);
- err = fuse_copy_one(&cs, &in->h, sizeof(in->h));
+ cs->req = req;
+ err = fuse_copy_one(cs, &in->h, sizeof(in->h));
if (!err)
- err = fuse_copy_args(&cs, in->numargs, in->argpages,
+ err = fuse_copy_args(cs, in->numargs, in->argpages,
(struct fuse_arg *) in->args, 0);
- fuse_copy_finish(&cs);
+ fuse_copy_finish(cs);
spin_lock(&fc->lock);
req->locked = 0;
if (req->aborted) {
@@ -986,6 +1030,105 @@ static ssize_t fuse_dev_read(struct kioc
return err;
}

+static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
+ unsigned long nr_segs, loff_t pos)
+{
+ struct fuse_copy_state cs;
+ struct file *file = iocb->ki_filp;
+ struct fuse_conn *fc = fuse_get_conn(file);
+ if (!fc)
+ return -EPERM;
+
+ fuse_copy_init(&cs, fc, 1, iov, nr_segs);
+
+ return fuse_dev_do_read(fc, file, &cs, iov_length(iov, nr_segs));
+}
+
+static int fuse_dev_pipe_buf_steal(struct pipe_inode_info *pipe,
+ struct pipe_buffer *buf)
+{
+ return 1;
+}
+
+static const struct pipe_buf_operations fuse_dev_pipe_buf_ops = {
+ .can_merge = 0,
+ .map = generic_pipe_buf_map,
+ .unmap = generic_pipe_buf_unmap,
+ .confirm = generic_pipe_buf_confirm,
+ .release = generic_pipe_buf_release,
+ .steal = fuse_dev_pipe_buf_steal,
+ .get = generic_pipe_buf_get,
+};
+
+static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe,
+ size_t len, unsigned int flags)
+{
+ int ret;
+ int page_nr = 0;
+ int do_wakeup = 0;
+ struct pipe_buffer bufs[PIPE_BUFFERS];
+ struct fuse_copy_state cs;
+ struct fuse_conn *fc = fuse_get_conn(in);
+ if (!fc)
+ return -EPERM;
+
+ fuse_copy_init(&cs, fc, 1, NULL, 0);
+ cs.pipebufs = bufs;
+ cs.pipe = pipe;
+ ret = fuse_dev_do_read(fc, in, &cs, len);
+ if (ret < 0)
+ goto out;
+
+ ret = 0;
+ pipe_lock(pipe);
+
+ if (!pipe->readers) {
+ send_sig(SIGPIPE, current, 0);
+ if (!ret)
+ ret = -EPIPE;
+ goto out_unlock;
+ }
+
+ if (pipe->nrbufs + cs.nr_segs > PIPE_BUFFERS) {
+ ret = -EIO;
+ goto out_unlock;
+ }
+
+ while (page_nr < cs.nr_segs) {
+ int newbuf = (pipe->curbuf + pipe->nrbufs) % PIPE_BUFFERS;
+ struct pipe_buffer *buf = pipe->bufs + newbuf;
+
+ buf->page = bufs[page_nr].page;
+ buf->offset = bufs[page_nr].offset;
+ buf->len = bufs[page_nr].len;
+ buf->ops = &fuse_dev_pipe_buf_ops;
+
+ pipe->nrbufs++;
+ page_nr++;
+ ret += buf->len;
+
+ if (pipe->inode)
+ do_wakeup = 1;
+ }
+
+out_unlock:
+ pipe_unlock(pipe);
+
+ if (do_wakeup) {
+ smp_mb();
+ if (waitqueue_active(&pipe->wait))
+ wake_up_interruptible(&pipe->wait);
+ kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
+ }
+
+out:
+ for (; page_nr < cs.nr_segs; page_nr++)
+ page_cache_release(bufs[page_nr].page);
+
+ return ret;
+}
+
static int fuse_notify_poll(struct fuse_conn *fc, unsigned int size,
struct fuse_copy_state *cs)
{
@@ -1246,7 +1389,7 @@ static ssize_t fuse_dev_write(struct kio
if (!fc)
return -EPERM;

- fuse_copy_init(&cs, fc, 0, NULL, iov, nr_segs);
+ fuse_copy_init(&cs, fc, 0, iov, nr_segs);

return fuse_dev_do_write(fc, &cs, iov_length(iov, nr_segs));
}
@@ -1306,11 +1449,8 @@ static ssize_t fuse_dev_splice_write(str
}
pipe_unlock(pipe);

- memset(&cs, 0, sizeof(struct fuse_copy_state));
- cs.fc = fc;
- cs.write = 0;
+ fuse_copy_init(&cs, fc, 0, NULL, nbuf);
cs.pipebufs = bufs;
- cs.nr_segs = nbuf;
cs.pipe = pipe;

if (flags & SPLICE_F_MOVE)
@@ -1467,6 +1607,7 @@ const struct file_operations fuse_dev_op
.llseek = no_llseek,
.read = do_sync_read,
.aio_read = fuse_dev_read,
+ .splice_read = fuse_dev_splice_read,
.write = do_sync_write,
.aio_write = fuse_dev_write,
.splice_write = fuse_dev_splice_write,

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