nbd: Improve error messages

This patch makes use of the Error object for nbd_receive_negotiate() so
that errors during negotiation look nicer.

Furthermore, this patch adds an additional error message if the received
magic was wrong, but would be correct for the other protocol version,
respectively: So if an export name was specified, but the NBD server
magic corresponds to an old handshake, this condition is explicitly
signaled to the user, and vice versa.

As these messages are now part of the "Could not open image" error
message, additional filtering has to be employed in iotest 083, which
this patch does as well.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 25 insertions, 17 deletions

diff --git a/nbd.c b/nbd.c
index 53cf82b..e56afbc1 100644
--- a/nbd.c
+++ b/nbd.c
@@ -494,7 +494,7 @@ fail:
 }
 
 int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
-                          off_t *size, size_t *blocksize)
+                          off_t *size, size_t *blocksize, Error **errp)
 {
     char buf[256];
     uint64_t magic, s;
@@ -506,13 +506,13 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
     rc = -EINVAL;
 
     if (read_sync(csock, buf, 8) != 8) {
-        LOG("read failed");
+        error_setg(errp, "Failed to read data");
         goto fail;
     }
 
     buf[8] = '\0';
     if (strlen(buf) == 0) {
-        LOG("server connection closed");
+        error_setg(errp, "Server connection closed unexpectedly");
         goto fail;
     }
 
@@ -527,12 +527,12 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
           qemu_isprint(buf[7]) ? buf[7] : '.');
 
     if (memcmp(buf, "NBDMAGIC", 8) != 0) {
-        LOG("Invalid magic received");
+        error_setg(errp, "Invalid magic received");
         goto fail;
     }
 
     if (read_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
-        LOG("read failed");
+        error_setg(errp, "Failed to read magic");
         goto fail;
     }
     magic = be64_to_cpu(magic);
@@ -545,52 +545,60 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
 
         TRACE("Checking magic (opts_magic)");
         if (magic != NBD_OPTS_MAGIC) {
-            LOG("Bad magic received");
+            if (magic == NBD_CLIENT_MAGIC) {
+                error_setg(errp, "Server does not support export names");
+            } else {
+                error_setg(errp, "Bad magic received");
+            }
             goto fail;
         }
         if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {
-            LOG("flags read failed");
+            error_setg(errp, "Failed to read server flags");
             goto fail;
         }
         *flags = be16_to_cpu(tmp) << 16;
         /* reserved for future use */
         if (write_sync(csock, &reserved, sizeof(reserved)) !=
             sizeof(reserved)) {
-            LOG("write failed (reserved)");
+            error_setg(errp, "Failed to read reserved field");
             goto fail;
         }
         /* write the export name */
         magic = cpu_to_be64(magic);
         if (write_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
-            LOG("write failed (magic)");
+            error_setg(errp, "Failed to send export name magic");
             goto fail;
         }
         opt = cpu_to_be32(NBD_OPT_EXPORT_NAME);
         if (write_sync(csock, &opt, sizeof(opt)) != sizeof(opt)) {
-            LOG("write failed (opt)");
+            error_setg(errp, "Failed to send export name option number");
             goto fail;
         }
         namesize = cpu_to_be32(strlen(name));
         if (write_sync(csock, &namesize, sizeof(namesize)) !=
             sizeof(namesize)) {
-            LOG("write failed (namesize)");
+            error_setg(errp, "Failed to send export name length");
             goto fail;
         }
         if (write_sync(csock, (char*)name, strlen(name)) != strlen(name)) {
-            LOG("write failed (name)");
+            error_setg(errp, "Failed to send export name");
             goto fail;
         }
     } else {
         TRACE("Checking magic (cli_magic)");
 
         if (magic != NBD_CLIENT_MAGIC) {
-            LOG("Bad magic received");
+            if (magic == NBD_OPTS_MAGIC) {
+                error_setg(errp, "Server requires an export name");
+            } else {
+                error_setg(errp, "Bad magic received");
+            }
             goto fail;
         }
     }
 
     if (read_sync(csock, &s, sizeof(s)) != sizeof(s)) {
-        LOG("read failed");
+        error_setg(errp, "Failed to read export length");
         goto fail;
     }
     *size = be64_to_cpu(s);
@@ -599,19 +607,19 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
 
     if (!name) {
         if (read_sync(csock, flags, sizeof(*flags)) != sizeof(*flags)) {
-            LOG("read failed (flags)");
+            error_setg(errp, "Failed to read export flags");
             goto fail;
         }
         *flags = be32_to_cpup(flags);
     } else {
         if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {
-            LOG("read failed (tmp)");
+            error_setg(errp, "Failed to read export flags");
             goto fail;
         }
         *flags |= be32_to_cpu(tmp);
     }
     if (read_sync(csock, &buf, 124) != 124) {
-        LOG("read failed (buf)");
+        error_setg(errp, "Failed to read reserved block");
         goto fail;
     }
     rc = 0;