fuse: return -ECONNABORTED on /dev/fuse read after abort

Currently the userspace has no way of knowing whether the fuse
connection ended because of umount or abort via sysfs. It makes it hard
for filesystems to free the mountpoint after abort without worrying
about removing some new mount.

The patch fixes it by returning different errors when userspace reads
from /dev/fuse (-ENODEV for umount and -ECONNABORTED for abort).

Add a new capability flag FUSE_ABORT_ERROR. If set and the connection is
gone because of sysfs abort, reading from the device will return
-ECONNABORTED.

Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 5d06384c2cae..78b6293bd04d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1234,9 +1234,10 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
 	if (err)
 		goto err_unlock;
 
-	err = -ENODEV;
-	if (!fiq->connected)
+	if (!fiq->connected) {
+		err = (fc->aborted && fc->abort_err) ? -ECONNABORTED : -ENODEV;
 		goto err_unlock;
+	}
 
 	if (!list_empty(&fiq->interrupts)) {
 		req = list_entry(fiq->interrupts.next, struct fuse_req,
@@ -1287,7 +1288,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
 	spin_lock(&fpq->lock);
 	clear_bit(FR_LOCKED, &req->flags);
 	if (!fpq->connected) {
-		err = -ENODEV;
+		err = (fc->aborted && fc->abort_err) ? -ECONNABORTED : -ENODEV;
 		goto out_end;
 	}
 	if (err) {
@@ -2076,7 +2077,7 @@ static void end_polls(struct fuse_conn *fc)
  * is OK, the request will in that case be removed from the list before we touch
  * it.
  */
-void fuse_abort_conn(struct fuse_conn *fc)
+void fuse_abort_conn(struct fuse_conn *fc, bool is_abort)
 {
 	struct fuse_iqueue *fiq = &fc->iq;
 
@@ -2089,6 +2090,7 @@ void fuse_abort_conn(struct fuse_conn *fc)
 
 		fc->connected = 0;
 		fc->blocked = 0;
+		fc->aborted = is_abort;
 		fuse_set_initialized(fc);
 		list_for_each_entry(fud, &fc->devices, entry) {
 			struct fuse_pqueue *fpq = &fud->pq;
@@ -2151,7 +2153,7 @@ int fuse_dev_release(struct inode *inode, struct file *file)
 		/* Are we the last open device? */
 		if (atomic_dec_and_test(&fc->dev_count)) {
 			WARN_ON(fc->iq.fasync != NULL);
-			fuse_abort_conn(fc);
+			fuse_abort_conn(fc, false);
 		}
 		fuse_dev_free(fud);
 	}