[Libguestfs] [libnbd PATCH 1/2] states: Track cmd->error as errno, not wire value

[Eric Blake]

We want to allow the block_status callback to be able to report a full
range of errno values, rather than the limited set of NBD_E* defined
in the protocol. To do so, we need to convert from wire error values
back into local errno values at a sooner point in the state machine.

This also changes a structured reply that includes more than one error
designation (theoretically possible at least for structured reads that
uses NBD_REPLY_TYPE_ERROR_OFFSET more than once to NBD_CMD_READ - even
if no existing NBD server actually does that) to preserve the first
error encountered, as that is often more interesting than any
follow-on errors.
---
 generator/states-reply-simple.c     | 2 +-
 generator/states-reply-structured.c | 4 +++-
 lib/aio.c                           | 1 -
 lib/internal.h                      | 2 +-
 4 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/generator/states-reply-simple.c b/generator/states-reply-simple.c
index e170482..7e5340c 100644
--- a/generator/states-reply-simple.c
+++ b/generator/states-reply-simple.c
@@ -45,7 +45,7 @@
     return 0;
   }

-  cmd->error = error;
+  cmd->error = nbd_internal_errno_of_nbd_error (error);
   if (cmd->error == 0 && cmd->type == NBD_CMD_READ) {
     h->rbuf = cmd->data;
     h->rlen = cmd->count;
diff --git a/generator/states-reply-structured.c b/generator/states-reply-structured.c
index c835713..c7ba892 100644
--- a/generator/states-reply-structured.c
+++ b/generator/states-reply-structured.c
@@ -179,7 +179,9 @@
     }
     assert (cmd); /* guaranteed by CHECK */

-    cmd->error = error;
+    /* Preserve first error encountered */
+    if (cmd->error == 0)
+      cmd->error = nbd_internal_errno_of_nbd_error (error);

     if (flags & NBD_REPLY_FLAG_DONE)
       SET_NEXT_STATE (%^FINISH_COMMAND);
diff --git a/lib/aio.c b/lib/aio.c
index a129af2..8361854 100644
--- a/lib/aio.c
+++ b/lib/aio.c
@@ -165,7 +165,6 @@ nbd_unlocked_aio_command_completed (struct nbd_handle *h,
     return 1;

   /* The command failed, set an error indication and return an error. */
-  error = nbd_internal_errno_of_nbd_error (error);
   set_error (error, "%s: command failed: %s",
              nbd_internal_name_of_nbd_cmd (type), strerror (error));
   return -1;
diff --git a/lib/internal.h b/lib/internal.h
index c1a57ac..45fc6df 100644
--- a/lib/internal.h
+++ b/lib/internal.h
@@ -223,7 +223,7 @@ struct command_in_flight {
   uint32_t count;
   void *data; /* Buffer for read/write, opaque for block status */
   extent_fn extent_fn;
-  uint32_t error;
+  uint32_t error; /* Local errno value */
 };

 /* crypto.c */
-- 
2.20.1