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, 1 insertions, 2 deletions

diff --git a/cmds-filesystem.c b/cmds-filesystem.c
index 045c896f..295592b0 100644
--- a/cmds-filesystem.c
+++ b/cmds-filesystem.c
@@ -478,8 +478,7 @@ static int cmd_resize(int argc, char **argv)
 	}
 
 	printf("Resize '%s' of '%s'\n", path, amount);
-	strncpy(args.name, amount, BTRFS_PATH_NAME_MAX);
-	args.name[BTRFS_PATH_NAME_MAX-1] = 0;
+	strncpy_null(args.name, amount);
 	res = ioctl(fd, BTRFS_IOC_RESIZE, &args);
 	e = errno;
 	close(fd);