From f141228d1b6baddadcd516137d76b3d852af8cde Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Tue, 12 Jan 2016 12:16:48 +0000
Subject: [PATCH 07/10] protocol: Send limited range of errno values to the
 client.

See the proposal here:
http://article.gmane.org/gmane.linux.drivers.nbd.general/3154

This implementation is based on Paolo Bonzini's for qemu-nbd:
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=ca4414804114fd0095b317785bc0b51862e62ebb
---
 TODO              |  6 ------
 src/connections.c | 36 +++++++++++++++++++++++++++++++++++-
 src/protocol.h    | 12 +++++++++++-
 3 files changed, 46 insertions(+), 8 deletions(-)

diff --git a/TODO b/TODO
index d39e64c..177a07c 100644
--- a/TODO
+++ b/TODO
@@ -1,9 +1,3 @@
-* There is a proposal to narrow the range of possible errnos that the
-  server can return, and also to encode them in an OS-independent way.
-  See: http://article.gmane.org/gmane.linux.drivers.nbd.general/3154
-  Implemented in QEMU already:
-  http://git.qemu.org/?p=qemu.git;a=commitdiff;h=ca4414804114fd0095b317785bc0b51862e62ebb
-
 * Can we do language bindings using #!'s?
   You would enter:
     nbdkit foo [args]
diff --git a/src/connections.c b/src/connections.c
index 6bdf4ef..f0a7662 100644
--- a/src/connections.c
+++ b/src/connections.c
@@ -639,6 +639,31 @@ skip_over_write_buffer (int sock, size_t count)
   }
 }
 
+/* Convert a system errno to an NBD_E* error code. */
+static int
+nbd_errno (int error)
+{
+  switch (error) {
+  case 0:
+    return NBD_SUCCESS;
+  case EPERM:
+    return NBD_EPERM;
+  case EIO:
+    return NBD_EIO;
+  case ENOMEM:
+    return NBD_ENOMEM;
+#ifdef EDQUOT
+  case EDQUOT:
+#endif
+  case EFBIG:
+  case ENOSPC:
+    return NBD_ENOSPC;
+  case EINVAL:
+  default:
+    return NBD_EINVAL;
+  }
+}
+
 static int
 recv_request_send_reply (struct connection *conn)
 {
@@ -722,7 +747,16 @@ recv_request_send_reply (struct connection *conn)
  send_reply:
   reply.magic = htobe32 (NBD_REPLY_MAGIC);
   reply.handle = request.handle;
-  reply.error = htobe32 (error);
+  reply.error = htobe32 (nbd_errno (error));
+
+  if (error != 0) {
+    /* Since we're about to send only the limited NBD_E* errno to the
+     * client, don't lose the information about what really happened
+     * on the server side.  Make sure there is a way for the operator
+     * to retrieve the real error.
+     */
+    debug ("sending error reply: %s", strerror (error));
+  }
 
   r = xwrite (conn->sockout, &reply, sizeof reply);
   if (r == -1) {
diff --git a/src/protocol.h b/src/protocol.h
index 2f9a341..fcbc145 100644
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -118,7 +118,7 @@ struct request {
 /* Reply (server -> client). */
 struct reply {
   uint32_t magic;               /* NBD_REPLY_MAGIC. */
-  uint32_t error;               /* 0 = ok, error code */
+  uint32_t error;               /* NBD_SUCCESS or one of NBD_E*. */
   uint64_t handle;              /* Opaque handle. */
 } __attribute__((packed));
 
@@ -133,4 +133,14 @@ struct reply {
 #define NBD_CMD_MASK_COMMAND 0xffff
 #define NBD_CMD_FLAG_FUA    (1<<16)
 
+/* Error codes (previously errno).
+ * See http://git.qemu.org/?p=qemu.git;a=commitdiff;h=ca4414804114fd0095b317785bc0b51862e62ebb
+ */
+#define NBD_SUCCESS     0
+#define NBD_EPERM       1
+#define NBD_EIO         5
+#define NBD_ENOMEM     12
+#define NBD_EINVAL     22
+#define NBD_ENOSPC     28
+
 #endif /* NBDKIT_PROTOCOL_H */
-- 
2.7.4