nbd: Add qemu-nbd -D for human-readable description

The NBD protocol allows servers to advertise a human-readable
description alongside an export name during NBD_OPT_LIST.  Add
an option to pass through the user's string to the NBD client.

Doing this also makes it easier to test commit 200650d4, which
is the client counterpart of receiving the description.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1476469998-28592-2-git-send-email-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 29 insertions, 10 deletions

diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index 93a6ca8549..7e78064021 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -104,9 +104,10 @@ static inline ssize_t read_sync(QIOChannel *ioc, void *buffer, size_t size)
     return nbd_wr_syncv(ioc, &iov, 1, size, true);
 }
 
-static inline ssize_t write_sync(QIOChannel *ioc, void *buffer, size_t size)
+static inline ssize_t write_sync(QIOChannel *ioc, const void *buffer,
+                                 size_t size)
 {
-    struct iovec iov = { .iov_base = buffer, .iov_len = size };
+    struct iovec iov = { .iov_base = (void *) buffer, .iov_len = size };
 
     return nbd_wr_syncv(ioc, &iov, 1, size, false);
 }
diff --git a/nbd/server.c b/nbd/server.c
index 36bcafcd50..ac42391b45 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -61,6 +61,7 @@ struct NBDExport {
 
     BlockBackend *blk;
     char *name;
+    char *description;
     off_t dev_offset;
     off_t size;
     uint16_t nbdflags;
@@ -129,7 +130,8 @@ static ssize_t nbd_negotiate_read(QIOChannel *ioc, void *buffer, size_t size)
 
 }
 
-static ssize_t nbd_negotiate_write(QIOChannel *ioc, void *buffer, size_t size)
+static ssize_t nbd_negotiate_write(QIOChannel *ioc, const void *buffer,
+                                   size_t size)
 {
     ssize_t ret;
     guint watch;
@@ -225,11 +227,15 @@ static int nbd_negotiate_send_rep(QIOChannel *ioc, uint32_t type, uint32_t opt)
 
 static int nbd_negotiate_send_rep_list(QIOChannel *ioc, NBDExport *exp)
 {
-    uint64_t magic, name_len;
+    uint64_t magic;
+    size_t name_len, desc_len;
     uint32_t opt, type, len;
+    const char *name = exp->name ? exp->name : "";
+    const char *desc = exp->description ? exp->description : "";
 
-    TRACE("Advertising export name '%s'", exp->name ? exp->name : "");
-    name_len = strlen(exp->name);
+    TRACE("Advertising export name '%s' description '%s'", name, desc);
+    name_len = strlen(name);
+    desc_len = strlen(desc);
     magic = cpu_to_be64(NBD_REP_MAGIC);
     if (nbd_negotiate_write(ioc, &magic, sizeof(magic)) != sizeof(magic)) {
         LOG("write failed (magic)");
@@ -245,18 +251,22 @@ static int nbd_negotiate_send_rep_list(QIOChannel *ioc, NBDExport *exp)
         LOG("write failed (reply type)");
         return -EINVAL;
     }
-    len = cpu_to_be32(name_len + sizeof(len));
+    len = cpu_to_be32(name_len + desc_len + sizeof(len));
     if (nbd_negotiate_write(ioc, &len, sizeof(len)) != sizeof(len)) {
         LOG("write failed (length)");
         return -EINVAL;
     }
     len = cpu_to_be32(name_len);
     if (nbd_negotiate_write(ioc, &len, sizeof(len)) != sizeof(len)) {
-        LOG("write failed (length)");
+        LOG("write failed (name length)");
+        return -EINVAL;
+    }
+    if (nbd_negotiate_write(ioc, name, name_len) != name_len) {
+        LOG("write failed (name buffer)");
         return -EINVAL;
     }
-    if (nbd_negotiate_write(ioc, exp->name, name_len) != name_len) {
-        LOG("write failed (buffer)");
+    if (nbd_negotiate_write(ioc, desc, desc_len) != desc_len) {
+        LOG("write failed (description buffer)");
         return -EINVAL;
     }
     return 0;
@@ -894,6 +904,12 @@ void nbd_export_set_name(NBDExport *exp, const char *name)
     nbd_export_put(exp);
 }
 
+void nbd_export_set_description(NBDExport *exp, const char *description)
+{
+    g_free(exp->description);
+    exp->description = g_strdup(description);
+}
+
 void nbd_export_close(NBDExport *exp)
 {
     NBDClient *client, *next;
@@ -903,6 +919,7 @@ void nbd_export_close(NBDExport *exp)
         client_close(client);
     }
     nbd_export_set_name(exp, NULL);
+    nbd_export_set_description(exp, NULL);
     nbd_export_put(exp);
 }
 
@@ -921,6 +938,7 @@ void nbd_export_put(NBDExport *exp)
 
     if (--exp->refcount == 0) {
         assert(exp->name == NULL);
+        assert(exp->description == NULL);
 
         if (exp->close) {
             exp->close(exp);