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, 20 insertions, 0 deletions

diff --git a/utils.c b/utils.c
index 7a1e39d7..f9ee8121 100644
--- a/utils.c
+++ b/utils.c
@@ -1126,6 +1126,26 @@ char *pretty_sizes(u64 size)
 }
 
 /*
+ * __strncpy__null - strncpy with null termination
+ * @dest:	the target array
+ * @src:	the source string
+ * @n:		maximum bytes to copy (size of *dest)
+ *
+ * Like strncpy, but ensures destination is null-terminated.
+ *
+ * Copies the string pointed to by src, including the terminating null
+ * byte ('\0'), to the buffer pointed to by dest, up to a maximum
+ * of n bytes.  Then ensure that dest is null-terminated.
+ */
+char *__strncpy__null(char *dest, const char *src, size_t n)
+{
+	strncpy(dest, src, n);
+	if (n > 0)
+		dest[n - 1] = '\0';
+	return dest;
+}
+
+/*
  * Checks to make sure that the label matches our requirements.
  * Returns:
        0    if everything is safe and usable