ceph: ref counted buffer

struct ceph_buffer is a simple ref-counted buffer.  We transparently
choose between kmalloc for small buffers and vmalloc for large ones.

This is currently used only for allocating memory for xattr data.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/buffer.c

+
+#include "ceph_debug.h"
+#include "buffer.h"
+
+struct ceph_buffer *ceph_buffer_new(gfp_t gfp)
+{
+	struct ceph_buffer *b;
+
+	b = kmalloc(sizeof(*b), gfp);
+	if (!b)
+		return NULL;
+	atomic_set(&b->nref, 1);
+	b->vec.iov_base = NULL;
+	b->vec.iov_len = 0;
+	b->alloc_len = 0;
+	return b;
+}
+
+int ceph_buffer_alloc(struct ceph_buffer *b, int len, gfp_t gfp)
+{
+	b->vec.iov_base = kmalloc(len, gfp | __GFP_NOWARN);
+	if (b->vec.iov_base) {
+		b->is_vmalloc = false;
+	} else {
+		b->vec.iov_base = __vmalloc(len, gfp, PAGE_KERNEL);
+		b->is_vmalloc = true;
+	}
+	if (!b->vec.iov_base)
+		return -ENOMEM;
+	b->alloc_len = len;
+	b->vec.iov_len = len;
+	return 0;
+}
+

fs/ceph/buffer.h

+#ifndef __FS_CEPH_BUFFER_H
+#define __FS_CEPH_BUFFER_H
+
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/types.h>
+#include <linux/uio.h>
+
+/*
+ * a simple reference counted buffer.
+ *
+ * use kmalloc for small sizes (<= one page), vmalloc for larger
+ * sizes.
+ */
+struct ceph_buffer {
+	atomic_t nref;
+	struct kvec vec;
+	size_t alloc_len;
+	bool is_vmalloc;
+};
+
+struct ceph_buffer *ceph_buffer_new(gfp_t gfp);
+int ceph_buffer_alloc(struct ceph_buffer *b, int len, gfp_t gfp);
+
+static inline struct ceph_buffer *ceph_buffer_get(struct ceph_buffer *b)
+{
+	atomic_inc(&b->nref);
+	return b;
+}
+
+static inline void ceph_buffer_put(struct ceph_buffer *b)
+{
+	if (b && atomic_dec_and_test(&b->nref)) {
+		if (b->vec.iov_base) {
+			if (b->is_vmalloc)
+				vfree(b->vec.iov_base);
+			else
+				kfree(b->vec.iov_base);
+		}
+		kfree(b);
+	}
+}
+
+static inline struct ceph_buffer *ceph_buffer_new_alloc(int len, gfp_t gfp)
+{
+	struct ceph_buffer *b = ceph_buffer_new(gfp);
+
+	if (b && ceph_buffer_alloc(b, len, gfp) < 0) {
+		ceph_buffer_put(b);
+		b = NULL;
+	}
+	return b;
+}
+
+#endif