Improve documentation of fuse_session_unmount

include/fuse.h

@@ -819,6 +819,8 @@ int fuse_mount(struct fuse *f, const char *mountpoint);
 /**
  * Unmount a FUSE file system.
  *
+ * See fuse_session_unmount() for additional information.
+ *
  * @param f the FUSE handle
  **/
 void fuse_unmount(struct fuse *f);

include/fuse_lowlevel.h

@@ -1850,7 +1850,26 @@ void fuse_session_reset(struct fuse_session *se);
 int fuse_session_exited(struct fuse_session *se);
 
 /**
- * Unmount the file system
+ * Ensure that file system is unmounted.
+ *
+ * In regular operation, the file system is typically unmounted by the
+ * user calling umount(8) or fusermount(1), which then terminates the
+ * FUSE session loop. However, the session loop may also terminate as
+ * a result of an explicit call to fuse_session_exit() (e.g. by a
+ * signal handler installed by fuse_set_signal_handler()). In this
+ * case the filesystem remains mounted, but any attempt to access it
+ * will block (while the filesystem process is still running) or give
+ * an ESHUTDOWN error (after the filesystem process has terminated).
+ *
+ * If the communication channel with the FUSE kernel module is still
+ * open (i.e., if the session loop was terminated by an explicit call
+ * to fuse_session_exit()), this function will close it and unmount
+ * the filesystem. If the communication channel has been closed by the
+ * kernel, this method will do (almost) nothing.
+ *
+ * NOTE: The above semantics mean that if the connection to the kernel
+ * is terminated via the ``/sys/fs/fuse/connections/NNN/abort`` file,
+ * this method will *not* unmount the filesystem.
  *
  * @param se the session
  */

lib/fuse_lowlevel.c

@@ -2655,6 +2655,8 @@ int fuse_session_receive_buf_int(struct fuse_session *se, struct fuse_buf *buf,
 
 	if (res == -1) {
 		if (err == ENODEV) {
+			/* Filesystem was unmounted, or connection was aborted
+			   via /sys/fs/fuse/connections */
 			fuse_session_exit(se);
 			return 0;
 		}
@@ -2743,6 +2745,8 @@ restart:
 			goto restart;
 
 		if (err == ENODEV) {
+			/* Filesystem was unmounted, or connection was aborted
+			   via /sys/fs/fuse/connections */
 			fuse_session_exit(se);
 			return 0;
 		}

lib/mount.c

@@ -275,7 +275,8 @@ void fuse_kern_unmount(const char *mountpoint, int fd)
 		close(fd);
 
 		/* If file poll returns POLLERR on the device file descriptor,
-		   then the filesystem is already unmounted */
+		   then the filesystem is already unmounted or the connection
+		   was severed via /sys/fs/fuse/connections/NNN/abort */
 		if (res == 1 && (pfd.revents & POLLERR))
 			return;
 	}