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, 5 insertions, 0 deletions

diff --git a/utils.h b/utils.h
index 2d2c23d2..bbcaf6a7 100644
--- a/utils.h
+++ b/utils.h
@@ -53,4 +53,9 @@ int get_device_info(int fd, u64 devid,
 		    struct btrfs_ioctl_dev_info_args *di_args);
 int get_fs_info(int fd, char *path, struct btrfs_ioctl_fs_info_args *fi_args,
 		struct btrfs_ioctl_dev_info_args **di_ret);
+
+char *__strncpy__null(char *dest, const char *src, size_t n);
+/* Helper to always get proper size of the destination string */
+#define strncpy_null(dest, src) __strncpy__null(dest, src, sizeof(dest))
+
 #endif