Re: [Nbd] Transforming stdin and stdout pair into a socket

Laurent Vivier
2009-05-11T08:03:43Z

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Le dimanche 10 mai 2009 à 21:19 +0300, Ciprian Dorin, Craciun a écrit :
> Hello all!

Hi,

perhaps the attached patch I wrote last year (november) is what you
want...

I didn't try to apply it to an up-to-date qemu-nbd.

Regards,
Laurent

> Today I've played around with NBD (Network Block Disk), and
> qemu-nbd (a NBD client that exports QEMU disks as NBD's).
>
> My problem is the following: both NBD kernel module and qemu-nbd
> implementation expect to use a socket in order to communicate.
> This means that in order to securely tunnel the connection over
> SSH (OpenSSH), I need an intermediary process that creates a socket
> and forwards all input / output between this socket and stdin / stdout
> (which are in fact pipes received from OpenSSH).
>
> My question is: can I somehow make the pair of stdin / stdout seem
> as a socket to the Linux syscalls (read and write)? (I would have to
> make stdin / stdout pair look like a single file descriptor.) (This
> would eliminate the intermediate process that just pipes data, and
> thus reduce the overhead.)
>
> Just to be clear: I know how to trick an application to have it's
> stdin and stdout be an opened socket (by using dup syscall). But in
> this case I need to trick the Linux kernel into thinking that stdin /
> stdout pair is a socket (or a single file descriptor).
>
> Thank you,
> Ciprian Craciun.
>
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--
------------------ Laurent.Vivier@bull.net ------------------
"Tout ce qui est impossible reste à accomplir" Jules Verne
"Things are only impossible until they're not" Jean-Luc Picard

[-- Attachment #2: qemu-nbd-inetd.patch --]
[-- Type: text/x-vhdl, Size: 3645 bytes --]

---
qemu-nbd.c | 41 +++++++++++++++++++++++++++++++++++------
1 file changed, 35 insertions(+), 6 deletions(-)

Index: qemu/qemu-nbd.c
===================================================================
--- qemu.orig/qemu-nbd.c 2008-09-11 17:06:05.000000000 +0200
+++ qemu/qemu-nbd.c 2008-09-15 16:10:37.000000000 +0200
@@ -57,6 +57,7 @@ static void usage(const char *name)
" -d, --disconnect disconnect the specified device\n"
" -e, --shared=NUM device can be shared by NUM clients (default '1')\n"
" -t, --persistent don't exit on the last connection\n"
+" -i, --inetd inetd interface: use stdin/stdout instead of a socke\n"
" -v, --verbose display extra debugging information\n"
" -h, --help display this help and exit\n"
" -V, --version output version information and exit\n"
@@ -183,14 +184,14 @@ int main(int argc, char **argv)
bool readonly = false;
bool disconnect = false;
const char *bindto = "0.0.0.0";
- int port = 1024;
+ int port = 0;
struct sockaddr_in addr;
socklen_t addr_len = sizeof(addr);
off_t fd_size;
char *device = NULL;
char *socket = NULL;
char sockpath[128];
- const char *sopt = "hVbo:p:rsnP:c:dvk:e:t";
+ const char *sopt = "hVbo:p:rsnP:c:dvk:e:ti";
struct option lopt[] = {
{ "help", 0, 0, 'h' },
{ "version", 0, 0, 'V' },
@@ -207,6 +208,7 @@ int main(int argc, char **argv)
{ "shared", 1, 0, 'e' },
{ "persistent", 0, 0, 't' },
{ "verbose", 0, 0, 'v' },
+ { "inetd", 0, 0, 'i' },
{ NULL, 0, 0, 0 }
};
int ch;
@@ -225,6 +227,7 @@ int main(int argc, char **argv)
int nb_fds = 0;
int max_fd;
int persistent = 0;
+ int inetd = 0;

while ((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
switch (ch) {
@@ -289,6 +292,9 @@ int main(int argc, char **argv)
case 't':
persistent = 1;
break;
+ case 'i':
+ inetd = 1;
+ break;
case 'v':
verbose = 1;
break;
@@ -326,6 +332,18 @@ int main(int argc, char **argv)
return 0;
}

+ if (inetd) {
+ if (shared != 1)
+ errx(EINVAL, "You cannot use inetd and shared");
+ if (socket)
+ errx(EINVAL, "You cannot use inetd and socket");
+ if (port)
+ errx(EINVAL, "You cannot use inetd and port");
+ } else {
+ if (!socket)
+ port = 1024;
+ }
+
bdrv_init();

bs = bdrv_new("hda");
@@ -412,9 +430,24 @@ int main(int argc, char **argv)
if (sharing_fds == NULL)
errx(ENOMEM, "Cannot allocate sharing fds");

+ data = qemu_memalign(512, NBD_BUFFER_SIZE);
+ if (data == NULL)
+ errx(ENOMEM, "Cannot allocate data buffer");
+
if (socket) {
sharing_fds[0] = unix_socket_incoming(socket);
} else {
+ if (inetd) {
+ /* read and write on stdin/stdout */
+ ret = nbd_negotiate(STDIN_FILENO, fd_size);
+ while (ret != -1) {
+ ret = nbd_trip(bs, STDIN_FILENO, fd_size, dev_offset,
+ &offset, readonly, data, NBD_BUFFER_SIZE);
+ }
+ qemu_free(data);
+ bdrv_close(bs);
+ return 0;
+ }
sharing_fds[0] = tcp_socket_incoming(bindto, port);
}

@@ -423,10 +456,6 @@ int main(int argc, char **argv)
max_fd = sharing_fds[0];
nb_fds++;

- data = qemu_memalign(512, NBD_BUFFER_SIZE);
- if (data == NULL)
- errx(ENOMEM, "Cannot allocate data buffer");
-
do {

FD_ZERO(&fds);