[PATCH] btrfs-progs: convert, warn if converting a fs which won't mount

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

On aarch64 with pagesize 64k, btrfs-convert of ext4 is successful,
but it won't mount because we don't yet support subpage blocksize/
sectorsize.

 BTRFS error (device vda): sectorsize 4096 not supported yet, only support 65536

So in this case during convert provide a warning and a 10s delay to
terminate the command.

For example:

WARNING: Blocksize 4096 is not equal to the pagesize 65536,
         converted filesystem won't mount on this system.
         The operation will start in 10 seconds. Use Ctrl-c to stop it.
10 9 8 7 6 5 4^C

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 convert/main.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/convert/main.c b/convert/main.c
index a04ec7a36abf..f936ec37d30a 100644
--- a/convert/main.c
+++ b/convert/main.c
@@ -1140,6 +1140,21 @@ static int do_convert(const char *devname, u32 convert_flags, u32 nodesize,
 		error("block size is too small: %u < 4096", blocksize);
 		goto fail;
 	}
+	if (blocksize != getpagesize()) {
+		int delay = 10;
+
+		warning("Blocksize %u is not equal to the pagesize %u,\n\
+         converted filesystem won't mount on this system.\n\
+         The operation will start in %d seconds. Use Ctrl-C to stop it.",
+			blocksize, getpagesize(), delay);
+
+		while (delay) {
+			printf("%2d", delay--);
+			fflush(stdout);
+			sleep(1);
+		}
+	}
+
 	if (btrfs_check_nodesize(nodesize, blocksize, features))
 		goto fail;
 	fd = open(devname, O_RDWR);
-- 
1.8.3.1