Document functions xmemdupz(), xread() and xwrite()

Signed-off-by: Heikki Orsila <heikki.orsila@iki.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -268,6 +268,12 @@ static inline void *xmalloc(size_t size)
 	return ret;
 }
 
+/*
+ * xmemdupz() allocates (len + 1) bytes of memory, duplicates "len" bytes of
+ * "data" to the allocated memory, zero terminates the allocated memory,
+ * and returns a pointer to the allocated memory. If the allocation fails,
+ * the program dies.
+ */
 static inline void *xmemdupz(const void *data, size_t len)
 {
 	char *p = xmalloc(len + 1);
@@ -329,6 +335,11 @@ static inline void *xmmap(void *start, size_t length,
 	return ret;
 }
 
+/*
+ * xread() is the same a read(), but it automatically restarts read()
+ * operations with a recoverable error (EAGAIN and EINTR). xread()
+ * DOES NOT GUARANTEE that "len" bytes is read even if the data is available.
+ */
 static inline ssize_t xread(int fd, void *buf, size_t len)
 {
 	ssize_t nr;
@@ -340,6 +351,11 @@ static inline ssize_t xread(int fd, void *buf, size_t len)
 	}
 }
 
+/*
+ * xwrite() is the same a write(), but it automatically restarts write()
+ * operations with a recoverable error (EAGAIN and EINTR). xwrite() DOES NOT
+ * GUARANTEE that "len" bytes is written even if the operation is successful.
+ */
 static inline ssize_t xwrite(int fd, const void *buf, size_t len)
 {
 	ssize_t nr;