[PATCH] btrfs-prog: scrub: print message when scrubbing a read-only filesystem without r option

[Li Zhang <zhanglikernel@gmail.com>]

issue:666

[enhancement]
When scrubbing a filesystem mounted read-only and without r
option, it aborts and there is no message associated with it.
So we need to print an error message when scrubbing a read-only
filesystem to tell the user what is going on here.

[implementation]
Move the error message from the main thread to each scrub thread,
previously the message was printed after all scrub threads
finished and without background mode.

[test]
Mount dev in read-only mode, then scrub it without r option

$ sudo mount /dev/vdb -o ro /mnt/
$ sudo btrfs scrub start  /mnt/
scrub started on /mnt/, fsid f7c26803-a68d-4a96-91c4-a629b57b7f64 (pid=2892)
Starting scrub on devid 1
Starting scrub on devid 2
Starting scrub on devid 3
scrub on devid 1 failed ret=-1 errno=30 (Read-only file system)
scrub on devid 2 failed ret=-1 errno=30 (Read-only file system)
scrub on devid 3 failed ret=-1 errno=30 (Read-only file system)

Signed-off-by: Li Zhang <zhanglikernel@gmail.com>
---
 cmds/scrub.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/cmds/scrub.c b/cmds/scrub.c
index d54e11f..e0400dd 100644
--- a/cmds/scrub.c
+++ b/cmds/scrub.c
@@ -957,7 +957,10 @@ static void *scrub_one_dev(void *ctx)
 		warning("setting ioprio failed: %m (ignored)");
 
 	ret = ioctl(sp->fd, BTRFS_IOC_SCRUB, &sp->scrub_args);
-        pr_verbose(LOG_DEFAULT, "scrub ioctl devid:%llu ret:%d errno:%d\n",sp->scrub_args.devid, ret, errno);
+	if (ret){
+		pr_verbose(LOG_DEFAULT, "scrub on devid %llu failed ret=%d errno=%d (%m)\n", 
+			sp->scrub_args.devid, ret, errno);
+	}
 	gettimeofday(&tv, NULL);
 	sp->ret = ret;
 	sp->stats.duration = tv.tv_sec - sp->stats.t_start;
@@ -1596,13 +1599,6 @@ static int scrub_start(const struct cmd_struct *cmd, int argc, char **argv,
 				++err;
 				break;
 			default:
-				if (do_print) {
-					errno = sp[i].ioctl_errno;
-					error(
-		"scrubbing %s failed for device id %lld: ret=%d, errno=%d (%m)",
-						path, devid, sp[i].ret,
-						sp[i].ioctl_errno);
-				}
 				++err;
 				continue;
 			}
-- 
1.8.3.1