fuse: support splice() reading from fuse device

Allow userspace filesystem implementation to use splice() to read from
the fuse device.

The userspace 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() call 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 rest of message to userspace buffer

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 187 insertions, 41 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index b070d3adf9b0..4413f5e7b133 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -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_copy_state *cs)
         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_copy_state *cs)
         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;
 
-                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--;
+                        if (cs->nr_segs == cs->pipe->buffers)
+                                return -EIO;
+
+                        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 == cs->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_copy_state *cs, struct page **pagep,
                 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 kiocb *iocb, const struct iovec *iov,
         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 kiocb *iocb, const struct iovec *iov,
         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 kiocb *iocb, const struct iovec *iov,
                 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 +1030,110 @@ static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
         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;
+        struct fuse_copy_state cs;
+        struct fuse_conn *fc = fuse_get_conn(in);
+        if (!fc)
+                return -EPERM;
+
+        bufs = kmalloc(pipe->buffers * sizeof (struct pipe_buffer), GFP_KERNEL);
+        if (!bufs)
+                return -ENOMEM;
+
+        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 - 1);
+                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);
+
+        kfree(bufs);
+        return ret;
+}
+
 static int fuse_notify_poll(struct fuse_conn *fc, unsigned int size,
                             struct fuse_copy_state *cs)
 {
@@ -1246,7 +1394,7 @@ static ssize_t fuse_dev_write(struct kiocb *iocb, const struct iovec *iov,
         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));
 }
@@ -1311,11 +1459,8 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
         }
         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)
@@ -1473,6 +1618,7 @@ const struct file_operations fuse_dev_operations = {
         .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,