fuse: implement poll support

Implement poll support.  Polled files are indexed using kh in a RB
tree rooted at fuse_conn->polled_files.

Client should send FUSE_NOTIFY_POLL notification once after processing
FUSE_POLL which has FUSE_POLL_SCHEDULE_NOTIFY set.  Sending
notification unconditionally after the latest poll or everytime file
content might have changed is inefficient but won't cause malfunction.

fuse_file_poll() can sleep and requires patches from the following
thread which allows f_op->poll() to sleep.

  http://thread.gmane.org/gmane.linux.kernel/726176

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

4 files changed, 172 insertions, 0 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ffd670bb8c8c..6176e444c76e 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -816,10 +816,29 @@ static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
         return err;
 }
 
+static int fuse_notify_poll(struct fuse_conn *fc, unsigned int size,
+                            struct fuse_copy_state *cs)
+{
+        struct fuse_notify_poll_wakeup_out outarg;
+        int err;
+
+        if (size != sizeof(outarg))
+                return -EINVAL;
+
+        err = fuse_copy_one(cs, &outarg, sizeof(outarg));
+        if (err)
+                return err;
+
+        return fuse_notify_poll_wakeup(fc, &outarg);
+}
+
 static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
                        unsigned int size, struct fuse_copy_state *cs)
 {
         switch (code) {
+        case FUSE_NOTIFY_POLL:
+                return fuse_notify_poll(fc, size, cs);
+
         default:
                 return -EINVAL;
         }
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index a28ced678d38..b3a944e4bb9c 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -62,6 +62,8 @@ struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
                         ff->kh = ++fc->khctr;
                         spin_unlock(&fc->lock);
                 }
+                RB_CLEAR_NODE(&ff->polled_node);
+                init_waitqueue_head(&ff->poll_wait);
         }
         return ff;
 }
@@ -170,7 +172,11 @@ int fuse_release_common(struct inode *inode, struct file *file, int isdir)
 
                 spin_lock(&fc->lock);
                 list_del(&ff->write_entry);
+                if (!RB_EMPTY_NODE(&ff->polled_node))
+                        rb_erase(&ff->polled_node, &fc->polled_files);
                 spin_unlock(&fc->lock);
+
+                wake_up_interruptible_sync(&ff->poll_wait);
                 /*
                  * Normally this will send the RELEASE request,
                  * however if some asynchronous READ or WRITE requests
@@ -1749,6 +1755,130 @@ static long fuse_file_compat_ioctl(struct file *file, unsigned int cmd,
         return fuse_file_do_ioctl(file, cmd, arg, FUSE_IOCTL_COMPAT);
 }
 
+/*
+ * All files which have been polled are linked to RB tree
+ * fuse_conn->polled_files which is indexed by kh.  Walk the tree and
+ * find the matching one.
+ */
+static struct rb_node **fuse_find_polled_node(struct fuse_conn *fc, u64 kh,
+                                              struct rb_node **parent_out)
+{
+        struct rb_node **link = &fc->polled_files.rb_node;
+        struct rb_node *last = NULL;
+
+        while (*link) {
+                struct fuse_file *ff;
+
+                last = *link;
+                ff = rb_entry(last, struct fuse_file, polled_node);
+
+                if (kh < ff->kh)
+                        link = &last->rb_left;
+                else if (kh > ff->kh)
+                        link = &last->rb_right;
+                else
+                        return link;
+        }
+
+        if (parent_out)
+                *parent_out = last;
+        return link;
+}
+
+/*
+ * The file is about to be polled.  Make sure it's on the polled_files
+ * RB tree.  Note that files once added to the polled_files tree are
+ * not removed before the file is released.  This is because a file
+ * polled once is likely to be polled again.
+ */
+static void fuse_register_polled_file(struct fuse_conn *fc,
+                                      struct fuse_file *ff)
+{
+        spin_lock(&fc->lock);
+        if (RB_EMPTY_NODE(&ff->polled_node)) {
+                struct rb_node **link, *parent;
+
+                link = fuse_find_polled_node(fc, ff->kh, &parent);
+                BUG_ON(*link);
+                rb_link_node(&ff->polled_node, parent, link);
+                rb_insert_color(&ff->polled_node, &fc->polled_files);
+        }
+        spin_unlock(&fc->lock);
+}
+
+static unsigned fuse_file_poll(struct file *file, poll_table *wait)
+{
+        struct inode *inode = file->f_dentry->d_inode;
+        struct fuse_file *ff = file->private_data;
+        struct fuse_conn *fc = get_fuse_conn(inode);
+        struct fuse_poll_in inarg = { .fh = ff->fh, .kh = ff->kh };
+        struct fuse_poll_out outarg;
+        struct fuse_req *req;
+        int err;
+
+        if (fc->no_poll)
+                return DEFAULT_POLLMASK;
+
+        poll_wait(file, &ff->poll_wait, wait);
+
+        /*
+         * Ask for notification iff there's someone waiting for it.
+         * The client may ignore the flag and always notify.
+         */
+        if (waitqueue_active(&ff->poll_wait)) {
+                inarg.flags |= FUSE_POLL_SCHEDULE_NOTIFY;
+                fuse_register_polled_file(fc, ff);
+        }
+
+        req = fuse_get_req(fc);
+        if (IS_ERR(req))
+                return PTR_ERR(req);
+
+        req->in.h.opcode = FUSE_POLL;
+        req->in.h.nodeid = get_node_id(inode);
+        req->in.numargs = 1;
+        req->in.args[0].size = sizeof(inarg);
+        req->in.args[0].value = &inarg;
+        req->out.numargs = 1;
+        req->out.args[0].size = sizeof(outarg);
+        req->out.args[0].value = &outarg;
+        request_send(fc, req);
+        err = req->out.h.error;
+        fuse_put_request(fc, req);
+
+        if (!err)
+                return outarg.revents;
+        if (err == -ENOSYS) {
+                fc->no_poll = 1;
+                return DEFAULT_POLLMASK;
+        }
+        return POLLERR;
+}
+
+/*
+ * This is called from fuse_handle_notify() on FUSE_NOTIFY_POLL and
+ * wakes up the poll waiters.
+ */
+int fuse_notify_poll_wakeup(struct fuse_conn *fc,
+                            struct fuse_notify_poll_wakeup_out *outarg)
+{
+        u64 kh = outarg->kh;
+        struct rb_node **link;
+
+        spin_lock(&fc->lock);
+
+        link = fuse_find_polled_node(fc, kh, NULL);
+        if (*link) {
+                struct fuse_file *ff;
+
+                ff = rb_entry(*link, struct fuse_file, polled_node);
+                wake_up_interruptible_sync(&ff->poll_wait);
+        }
+
+        spin_unlock(&fc->lock);
+        return 0;
+}
+
 static const struct file_operations fuse_file_operations = {
         .llseek         = fuse_file_llseek,
         .read           = do_sync_read,
@@ -1765,6 +1895,7 @@ static const struct file_operations fuse_file_operations = {
         .splice_read    = generic_file_splice_read,
         .unlocked_ioctl = fuse_file_ioctl,
         .compat_ioctl   = fuse_file_compat_ioctl,
+        .poll           = fuse_file_poll,
 };
 
 static const struct file_operations fuse_direct_io_file_operations = {
@@ -1779,6 +1910,7 @@ static const struct file_operations fuse_direct_io_file_operations = {
         .flock          = fuse_file_flock,
         .unlocked_ioctl = fuse_file_ioctl,
         .compat_ioctl   = fuse_file_compat_ioctl,
+        .poll           = fuse_file_poll,
         /* no mmap and splice_read */
 };
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 86f013303828..986fbd4c1ff5 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -19,6 +19,8 @@
 #include <linux/backing-dev.h>
 #include <linux/mutex.h>
 #include <linux/rwsem.h>
+#include <linux/rbtree.h>
+#include <linux/poll.h>
 
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
@@ -111,6 +113,12 @@ struct fuse_file {
 
         /** Entry on inode's write_files list */
         struct list_head write_entry;
+
+        /** RB node to be linked on fuse_conn->polled_files */
+        struct rb_node polled_node;
+
+        /** Wait queue head for poll */
+        wait_queue_head_t poll_wait;
 };
 
 /** One input argument of a request */
@@ -328,6 +336,9 @@ struct fuse_conn {
         /** The next unique kernel file handle */
         u64 khctr;
 
+        /** rbtree of fuse_files waiting for poll events indexed by ph */
+        struct rb_root polled_files;
+
         /** Number of requests currently in the background */
         unsigned num_background;
 
@@ -416,6 +427,9 @@ struct fuse_conn {
         /** Is bmap not implemented by fs? */
         unsigned no_bmap:1;
 
+        /** Is poll not implemented by fs? */
+        unsigned no_poll:1;
+
         /** Do multi-page cached writes */
         unsigned big_writes:1;
 
@@ -525,6 +539,12 @@ int fuse_fsync_common(struct file *file, struct dentry *de, int datasync,
                       int isdir);
 
 /**
+ * Notify poll wakeup
+ */
+int fuse_notify_poll_wakeup(struct fuse_conn *fc,
+                            struct fuse_notify_poll_wakeup_out *outarg);
+
+/**
  * Initialize file operations on a regular file
  */
 void fuse_init_file_inode(struct inode *inode);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 0e15bc221d23..ba7256128084 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -486,6 +486,7 @@ static struct fuse_conn *new_conn(struct super_block *sb)
                 /* fuse does it's own writeback accounting */
                 fc->bdi.capabilities = BDI_CAP_NO_ACCT_WB;
                 fc->khctr = 0;
+                fc->polled_files = RB_ROOT;
                 fc->dev = sb->s_dev;
                 err = bdi_init(&fc->bdi);
                 if (err)