nbd: support feature negotiation

nbd supports writing flags in bytes 24...27 of the header,
and uses that for the read-only flag.  Add support for it
in qemu-nbd.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/nbd.c

@@ -48,6 +48,7 @@
 
 typedef struct BDRVNBDState {
     int sock;
+    uint32_t nbdflags;
     off_t size;
     size_t blocksize;
     char *export_name; /* An NBD server may export several devices */
@@ -111,7 +112,6 @@ static int nbd_establish_connection(BlockDriverState *bs)
     int ret;
     off_t size;
     size_t blocksize;
-    uint32_t nbdflags;
 
     if (s->host_spec[0] == '/') {
         sock = unix_socket_outgoing(s->host_spec);
@@ -126,7 +126,7 @@ static int nbd_establish_connection(BlockDriverState *bs)
     }
 
     /* NBD handshake */
-    ret = nbd_receive_negotiate(sock, s->export_name, &nbdflags, &size,
+    ret = nbd_receive_negotiate(sock, s->export_name, &s->nbdflags, &size,
                                 &blocksize);
     if (ret == -1) {
         logout("Failed to negotiate with the NBD server\n");

nbd.c

@@ -30,6 +30,10 @@
 #include <ctype.h>
 #include <inttypes.h>
 
+#ifdef __linux__
+#include <linux/fs.h>
+#endif
+
 #include "qemu_socket.h"
 
 //#define DEBUG_NBD
@@ -172,7 +176,7 @@ int unix_socket_outgoing(const char *path)
                   Request (type == 2)
 */
 
-int nbd_negotiate(int csock, off_t size)
+int nbd_negotiate(int csock, off_t size, uint32_t flags)
 {
     char buf[8 + 8 + 8 + 128];
 
@@ -180,14 +184,16 @@ int nbd_negotiate(int csock, off_t size)
         [ 0 ..   7]   passwd   ("NBDMAGIC")
         [ 8 ..  15]   magic    (0x00420281861253)
         [16 ..  23]   size
-        [24 .. 151]   reserved (0)
+        [24 ..  27]   flags
+        [28 .. 151]   reserved (0)
      */
 
     TRACE("Beginning negotiation.");
     memcpy(buf, "NBDMAGIC", 8);
     cpu_to_be64w((uint64_t*)(buf + 8), 0x00420281861253LL);
     cpu_to_be64w((uint64_t*)(buf + 16), size);
-    memset(buf + 24, 0, 128);
+    cpu_to_be32w((uint32_t*)(buf + 24), flags | NBD_FLAG_HAS_FLAGS);
+    memset(buf + 28, 0, 124);
 
     if (write_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {
         LOG("write failed");
@@ -337,8 +343,8 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
         return 0;
 }
 
-#ifndef _WIN32
-int nbd_init(int fd, int csock, off_t size, size_t blocksize)
+#ifdef __linux__
+int nbd_init(int fd, int csock, uint32_t flags, off_t size, size_t blocksize)
 {
     TRACE("Setting block size to %lu", (unsigned long)blocksize);
 
@@ -358,6 +364,18 @@ int nbd_init(int fd, int csock, off_t size, size_t blocksize)
         return -1;
     }
 
+    if (flags & NBD_FLAG_READ_ONLY) {
+        int read_only = 1;
+        TRACE("Setting readonly attribute");
+
+        if (ioctl(fd, BLKROSET, (unsigned long) &read_only) < 0) {
+            int serrno = errno;
+            LOG("Failed setting read-only attribute");
+            errno = serrno;
+            return -1;
+        }
+    }
+
     TRACE("Clearing NBD socket");
 
     if (ioctl(fd, NBD_CLEAR_SOCK) == -1) {
@@ -548,7 +566,7 @@ static int nbd_send_reply(int csock, struct nbd_reply *reply)
 }
 
 int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
-             off_t *offset, bool readonly, uint8_t *data, int data_size)
+             off_t *offset, uint32_t nbdflags, uint8_t *data, int data_size)
 {
     struct nbd_request request;
     struct nbd_reply reply;
@@ -632,7 +650,7 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
             return -1;
         }
 
-        if (readonly) {
+        if (nbdflags & NBD_FLAG_READ_ONLY) {
             TRACE("Server is read-only, return error");
             reply.error = 1;
         } else {

nbd.h

@@ -37,6 +37,9 @@ struct nbd_reply {
     uint64_t handle;
 } QEMU_PACKED;
 
+#define NBD_FLAG_HAS_FLAGS      (1 << 0)        /* Flags are there */
+#define NBD_FLAG_READ_ONLY      (1 << 1)        /* Device is read-only */
+
 enum {
     NBD_CMD_READ = 0,
     NBD_CMD_WRITE = 1,
@@ -53,14 +56,14 @@ int tcp_socket_incoming_spec(const char *address_and_port);
 int unix_socket_outgoing(const char *path);
 int unix_socket_incoming(const char *path);
 
-int nbd_negotiate(int csock, off_t size);
+int nbd_negotiate(int csock, off_t size, uint32_t flags);
 int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
                           off_t *size, size_t *blocksize);
-int nbd_init(int fd, int csock, off_t size, size_t blocksize);
+int nbd_init(int fd, int csock, uint32_t flags, off_t size, size_t blocksize);
 int nbd_send_request(int csock, struct nbd_request *request);
 int nbd_receive_reply(int csock, struct nbd_reply *reply);
 int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
-             off_t *offset, bool readonly, uint8_t *data, int data_size);
+             off_t *offset, uint32_t nbdflags, uint8_t *data, int data_size);
 int nbd_client(int fd);
 int nbd_disconnect(int fd);
 

qemu-nbd.c

@@ -185,7 +185,7 @@ int main(int argc, char **argv)
     BlockDriverState *bs;
     off_t dev_offset = 0;
     off_t offset = 0;
-    bool readonly = false;
+    uint32_t nbdflags = 0;
     bool disconnect = false;
     const char *bindto = "0.0.0.0";
     int port = NBD_DEFAULT_PORT;
@@ -230,7 +230,6 @@ int main(int argc, char **argv)
     int nb_fds = 0;
     int max_fd;
     int persistent = 0;
-    uint32_t nbdflags;
 
     while ((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
         switch (ch) {
@@ -263,7 +262,7 @@ int main(int argc, char **argv)
             }
             break;
         case 'r':
-            readonly = true;
+            nbdflags |= NBD_FLAG_READ_ONLY;
             flags &= ~BDRV_O_RDWR;
             break;
         case 'P':
@@ -398,13 +397,13 @@ int main(int argc, char **argv)
             }
 
             ret = nbd_receive_negotiate(sock, NULL, &nbdflags,
-					&size, &blocksize);
+                                        &size, &blocksize);
             if (ret == -1) {
                 ret = 1;
                 goto out;
             }
 
-            ret = nbd_init(fd, sock, size, blocksize);
+            ret = nbd_init(fd, sock, nbdflags, size, blocksize);
             if (ret == -1) {
                 ret = 1;
                 goto out;
@@ -463,7 +462,7 @@ int main(int argc, char **argv)
         for (i = 1; i < nb_fds && ret; i++) {
             if (FD_ISSET(sharing_fds[i], &fds)) {
                 if (nbd_trip(bs, sharing_fds[i], fd_size, dev_offset,
-                    &offset, readonly, data, NBD_BUFFER_SIZE) != 0) {
+                    &offset, nbdflags, data, NBD_BUFFER_SIZE) != 0) {
                     close(sharing_fds[i]);
                     nb_fds--;
                     sharing_fds[i] = sharing_fds[nb_fds];
@@ -479,7 +478,7 @@ int main(int argc, char **argv)
                                              (struct sockaddr *)&addr,
                                              &addr_len);
                 if (sharing_fds[nb_fds] != -1 &&
-                    nbd_negotiate(sharing_fds[nb_fds], fd_size) != -1) {
+                    nbd_negotiate(sharing_fds[nb_fds], fd_size, nbdflags) != -1) {
                         if (sharing_fds[nb_fds] > max_fd)
                             max_fd = sharing_fds[nb_fds];
                         nb_fds++;