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 <[email protected]>
Message-Id: <1476469998[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

diff --git a/include/block/nbd.h b/include/block/nbd.h
index 80610ff31bfec3e8954670aed3a2414d5f289a47..fd58390d5d19844a52329cda4f473fdaffc84c3b 100644 (file)
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -115,6 +115,7 @@ BlockBackend *nbd_export_get_blockdev(NBDExport *exp);
 
 NBDExport *nbd_export_find(const char *name);
 void nbd_export_set_name(NBDExport *exp, const char *name);
+void nbd_export_set_description(NBDExport *exp, const char *description);
 void nbd_export_close_all(void);
 
 void nbd_client_new(NBDExport *exp,

diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index 93a6ca8549e8ff9e50c9bd94e0eadb369a2e399f..7e78064021ed54017354c400001e177f1c3c4ad6 100644 (file)
--- 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 36bcafcd5060b9ce5d178b7ce4b845b087a0bf30..ac42391b45126559cb113d14357f527d61c47492 100644 (file)
--- 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);

diff --git a/qemu-nbd.c b/qemu-nbd.c
index b757dc76218d080a39a3db0e0ea8ae0ef3cc8688..c734f627b4b3845c8d3adb78c8ba5d22098cbf27 100644 (file)
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -83,6 +83,7 @@ static void usage(const char *name)
 "  -t, --persistent          don't exit on the last connection\n"
 "  -v, --verbose             display extra debugging information\n"
 "  -x, --export-name=NAME    expose export by name\n"
+"  -D, --description=TEXT    with -x, also export a human-readable description\n"
 "\n"
 "Exposing part of the image:\n"
 "  -o, --offset=OFFSET       offset into the image\n"
@@ -477,7 +478,7 @@ int main(int argc, char **argv)
     off_t fd_size;
     QemuOpts *sn_opts = NULL;
     const char *sn_id_or_name = NULL;
-    const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:tl:x:T:";
+    const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:tl:x:T:D:";
     struct option lopt[] = {
         { "help", no_argument, NULL, 'h' },
         { "version", no_argument, NULL, 'V' },
@@ -503,6 +504,7 @@ int main(int argc, char **argv)
         { "verbose", no_argument, NULL, 'v' },
         { "object", required_argument, NULL, QEMU_NBD_OPT_OBJECT },
         { "export-name", required_argument, NULL, 'x' },
+        { "description", required_argument, NULL, 'D' },
         { "tls-creds", required_argument, NULL, QEMU_NBD_OPT_TLSCREDS },
         { "image-opts", no_argument, NULL, QEMU_NBD_OPT_IMAGE_OPTS },
         { "trace", required_argument, NULL, 'T' },
@@ -524,6 +526,7 @@ int main(int argc, char **argv)
     BlockdevDetectZeroesOptions detect_zeroes = BLOCKDEV_DETECT_ZEROES_OPTIONS_OFF;
     QDict *options = NULL;
     const char *export_name = NULL;
+    const char *export_description = NULL;
     const char *tlscredsid = NULL;
     bool imageOpts = false;
     bool writethrough = true;
@@ -689,6 +692,9 @@ int main(int argc, char **argv)
         case 'x':
             export_name = optarg;
             break;
+        case 'D':
+            export_description = optarg;
+            break;
         case 'v':
             verbose = 1;
             break;
@@ -937,7 +943,11 @@ int main(int argc, char **argv)
     }
     if (export_name) {
         nbd_export_set_name(exp, export_name);
+        nbd_export_set_description(exp, export_description);
         newproto = true;
+    } else if (export_description) {
+        error_report("Export description requires an export name");
+        exit(EXIT_FAILURE);
     }
 
     server_ioc = qio_channel_socket_new();

diff --git a/qemu-nbd.texi b/qemu-nbd.texi
index b7a9c6d02f7430ec7fe1a88f552d1e7326cdc069..9a84e81eed9c82a7bc62451151659366f79c20db 100644 (file)
--- a/qemu-nbd.texi
+++ b/qemu-nbd.texi
@@ -79,9 +79,12 @@ Disconnect the device @var{dev}
 Allow up to @var{num} clients to share the device (default @samp{1})
 @item -t, --persistent
 Don't exit on the last connection
-@item -x NAME, --export-name=NAME
+@item -x, --export-name=@var{name}
 Set the NBD volume export name. This switches the server to use
 the new style NBD protocol negotiation
+@item -D, --description=@var{description}
+Set the NBD volume export description, as a human-readable
+string. Requires the use of @option{-x}
 @item --tls-creds=ID
 Enable mandatory TLS encryption for the server by setting the ID
 of the TLS credentials object previously created with the --object