btrfs-progs: simplify ioctl name copy and null termination

In the places where we copy a string into the name
member of btrfs_ioctl_vol_args or btrfs_ioctl_vol_args_v2,
we use strncopy (to not overflow the name array) and then
set the last position to the null character.

Howver, in both cases the arrays are defined with:

        char name[MAX+1];

hence the last array position is name[MAX].

In most cases, we now insert the null at name[MAX-1]
which deprives us of one useful character.

Even the above isn't consistent through the code, so
make some helper code to make it simple, i.e.
strncpy_null(dest, src) which automatically does the
right thing based on the size of dest.

Thanks to Zach Brown for the macro suggestion.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/btrfsctl.c b/btrfsctl.c
index 049a5f35..8fd8cc32 100644
--- a/btrfsctl.c
+++ b/btrfsctl.c
@@ -242,10 +242,9 @@ int main(int ac, char **av)
 		fd = btrfsctl_open_file_or_dir(fname);
 	 }
 
-	if (name) {
-                strncpy(args.name, name, BTRFS_PATH_NAME_MAX + 1);
-                args.name[BTRFS_PATH_NAME_MAX] = 0;
-	} else
+	if (name)
+		strncpy_null(args.name, name);
+	else
 		args.name[0] = '\0';
 
 	if (command == BTRFS_IOC_SNAP_CREATE) {