[PATCH] btrfs-progs: handle balance and replace concurrency

[Anand Jain <anand.jain@oracle.com>]

Test case:
Run replace
 btrfs repl start -B -f /dev/sdd /dev/sdb /btrfs;
while replace is still running, from another terminal try to start
balance
 btrfs bal start  --full-balance /btrfs; echo ...:$?
 Done, had to relocate 0 out of 0 chunks
 ...:0

which fails to report that balance failed to relocate because another
exclusive operation is running.
In fact kernel ioctl BTRFS_IOC_BALANCE(_V2) does return error code 8,
but progs recast it to 0. Fix it by checking for the error code > 0.

After:
 btrfs bal start --full-balance /btrfs; echo ...:$?
 ERROR: balance: add/delete/balance/replace/resize operation in progress
 ...:8

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 cmds-balance.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/cmds-balance.c b/cmds-balance.c
index 6cc26c358f95..77402ef62d85 100644
--- a/cmds-balance.c
+++ b/cmds-balance.c
@@ -481,11 +481,12 @@ static int do_balance(const char *path, struct btrfs_ioctl_balance_args *args,
 			"There may be more info in syslog - try dmesg | tail\n");
 			ret = 1;
 		}
+	} else if (ret > 0) {
+		error("balance: %s", btrfs_err_str(ret));
 	} else {
 		printf("Done, had to relocate %llu out of %llu chunks\n",
 		       (unsigned long long)args->stat.completed,
 		       (unsigned long long)args->stat.considered);
-		ret = 0;
 	}
 
 out:
-- 
1.8.3.1