[PATCH v3 04/16] libceph: define ceph_extract_encoded_string()

[Alex Elder <elder@inktank.com>]

This adds a new utility routine which will return a dynamically-
allocated buffer containing a string that has been decoded from ceph
over-the-wire format.  It also returns the length of the string
if the address of a size variable is supplied to receive it.

Signed-off-by: Alex Elder <elder@inktank.com>
---
v3: Final version.  Sage convinced me that there was no need for
    ceph_decode_string() other than its use in this function, so
    now this implements what that function had been doing directly.

 include/linux/ceph/decode.h |   44
++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

Index: b/include/linux/ceph/decode.h
===================================================================
--- a/include/linux/ceph/decode.h
+++ b/include/linux/ceph/decode.h
@@ -85,6 +85,50 @@ static inline int ceph_has_room(void **p
 	} while (0)

 /*
+ * Allocate a buffer big enough to hold the wire-encoded string, and
+ * decode the string into it.  The resulting string will always be
+ * terminated with '\0'.  If successful, *p will be advanced
+ * past the decoded data.  Also, if lenp is not a null pointer, the
+ * length (not including the terminating '\0') will be recorded in
+ * *lenp.  Note that a zero-length string is a valid return value.
+ *
+ * Returns a pointer to the newly-allocated string buffer, or a null
+ * pointer if an error occurs.  Neither *p nor *lenp will have been
+ * updated if NULL is returned.
+ *
+ * There are two possible failures:
+ *   - converting the string would require accessing memory at or
+ *     beyond the "end" pointer provided
+ *   - memory could not be allocated for the result
+ */
+static inline char *ceph_extract_encoded_string(void **p, void *end,
+						size_t *lenp, gfp_t gfp)
+{
+	u32 len;
+	void *sp = *p;
+	char *buf = NULL;
+
+	ceph_decode_32_safe(&sp, end, len, out);
+	if (!ceph_has_room(&sp, end, len))
+		return NULL;
+
+	buf = kmalloc(len + 1, gfp);
+	if (!buf)
+		return NULL;
+
+	if (len)
+		memcpy(buf, sp, len);
+	buf[len] = '\0';
+
+	*p = (char *) *p + sizeof (u32) + len;
+
+	if (lenp)
+		*lenp = (size_t) len;
+out:
+	return buf;
+}
+
+/*
  * struct ceph_timespec <-> struct timespec
  */
 static inline void ceph_decode_timespec(struct timespec *ts,