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, 6 deletions

diff --git a/cmds-device.c b/cmds-device.c
index 7a0f7a40..198ad689 100644
--- a/cmds-device.c
+++ b/cmds-device.c
@@ -116,8 +116,7 @@ static int cmd_add_dev(int argc, char **argv)
 		}
 		close(devfd);
 
-		strncpy(ioctl_args.name, argv[i], BTRFS_PATH_NAME_MAX);
-		ioctl_args.name[BTRFS_PATH_NAME_MAX-1] = 0;
+		strncpy_null(ioctl_args.name, argv[i]);
 		res = ioctl(fdmnt, BTRFS_IOC_ADD_DEV, &ioctl_args);
 		e = errno;
 		if(res<0){
@@ -161,8 +160,7 @@ static int cmd_rm_dev(int argc, char **argv)
 		struct	btrfs_ioctl_vol_args arg;
 		int	res;
 
-		strncpy(arg.name, argv[i], BTRFS_PATH_NAME_MAX);
-		arg.name[BTRFS_PATH_NAME_MAX-1] = 0;
+		strncpy_null(arg.name, argv[i]);
 		res = ioctl(fdmnt, BTRFS_IOC_RM_DEV, &arg);
 		e = errno;
 		if(res<0){
@@ -227,8 +225,7 @@ static int cmd_scan_dev(int argc, char **argv)
 
 		printf("Scanning for Btrfs filesystems in '%s'\n", argv[i]);
 
-		strncpy(args.name, argv[i], BTRFS_PATH_NAME_MAX);
-		args.name[BTRFS_PATH_NAME_MAX-1] = 0;
+		strncpy_null(args.name, argv[i]);
 		/*
 		 * FIXME: which are the error code returned by this ioctl ?
 		 * it seems that is impossible to understand if there no is