On Monday 13 September 2010 02:51, Rob Landley wrote:
> Finally got some time to debug this, and it now actually works.
>
> nbd 1.2.3.4 9876 /dev/nbd0
> mount /dev/nbd0 /blah
>
> It's not busyboxified at all (standalone, no external dependencies). If a
> server exports multiple NBDs it only supports selecting them by port number
> (there's an extention to select them by name; I didn't need it so didn't
> implement it).
>
> Its command line option parsing is somewhere between "pathetic" and
> "nonexistent", so there's no if() around the call to daemon() and such, and
> the 4k block size is hardwired (which means with an MTU of 1500 the packets
> will be split, but just about all modern filesystems are using a 4k block
> size
> anyway and gigabit ethernet with a 1500 byte mtu is silly).
>
> But it Worked For Me.
>
> Denys: you wanna busyboxify it, or wait for me to get around to it now that
> my
> immediate need for something working is satisfied? :)
I am attaching the busyboxified version.
Outer for(;;) loop looks wrong. For one, on the second iteration
nbd file descriptor will be closed. I have doubts ioctls can work
on closed fds. Repeatedly daemonizing also looks strange.
I imagine the loop should just be removed, body should execute just once.
// Open the device to force reread of the partition table.
if (!fork()) {
char *s = strrchr(device, '/');
sprintf(data, "/sys/block/%.32s/pid", s ? s+1 : device);
// Is it up yet?
for (;;) {
temp = open(data, O_RDONLY);
if (temp == -1) sleep(1);
else {
close(temp);
break;
}
}
close(open(device, O_RDONLY));
exit(0);
}
Why do you do it in a child? nbd-client's parent might actually
prefer to know that this step is complete before nbd-client
exits. As it stands, now reread happens "somewhere in the future,
maybe in 2050, who knows".
// Process NBD requests until further notice.
if (ioctl(nbd, NBD_DO_IT)>=0 || errno==EBADR) break;
Need more comments here.
Does this ioctl block for a long time, processing many requests?
On what condition does it return? Etc.
--
vda
/*
* Copyright 2010 Rob Landley <[email protected]>
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
#include "libbb.h"
#include <netinet/tcp.h>
#include <linux/fs.h>
//applet:IF_NBDCLIENT(APPLET_ODDNAME(nbd-client, nbdclient, _BB_DIR_USR_SBIN,
_BB_SUID_DROP, nbdclient))
//kbuild:lib-$(CONFIG_NBDCLIENT) += nbd-client.o
//config:config NBDCLIENT
//config: bool "nbd-client"
//config: default y
//config: help
//config: Network block device client
#define NBD_SET_SOCK _IO(0xab, 0)
#define NBD_SET_BLKSIZE _IO(0xab, 1)
#define NBD_SET_SIZE _IO(0xab, 2)
#define NBD_DO_IT _IO(0xab, 3)
#define NBD_CLEAR_SOCK _IO(0xab, 4)
#define NBD_CLEAR_QUEUE _IO(0xab, 5)
#define NBD_PRINT_DEBUG _IO(0xab, 6)
#define NBD_SET_SIZE_BLOCKS _IO(0xab, 7)
#define NBD_DISCONNECT _IO(0xab, 8)
#define NBD_SET_TIMEOUT _IO(0xab, 9)
//usage:#define nbdclient_trivial_usage
//usage: "HOST PORT BLOCKDEV"
//usage:#define nbdclient_full_usage "\n\n"
//usage: "Connect to HOST and provide a network block device on BLOCKDEV"
//TODO: more compat with nbd-client version 2.9.13. It says:
// Usage: nbd-client [bs=blocksize] [timeout=sec] host port nbd_device [-swap]
[-persist] [-nofork]
// Or : nbd-client -d nbd_device
// Or : nbd-client -c nbd_device
// Default value for blocksize is 1024 (recommended for ethernet)
// Allowed values for blocksize are 512,1024,2048,4096
// Note, that kernel 2.4.2 and older ones do not work correctly with
// blocksizes other than 1024 without patches
int nbdclient_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int nbdclient_main(int argc, char **argv)
{
int sock, nbd;
unsigned long timeout = 0;
char *host, *port, *device;
struct nbd_header_t {
uint64_t magic1; /* "NBDMAGIC" */
uint64_t magic2; /* 0x420281861253 big endian */
uint64_t devsize;
uint32_t flags;
char data[124];
} nbd_header;
struct bug_check {
char c[offsetof(struct nbd_header_t, data) == 8+8+8+4 ? 1 : -1];
};
// Parse command line stuff (just a stub now)
if (argc != 4)
bb_show_usage();
host = argv[1];
port = argv[2];
device = argv[3];
// Make sure the /dev/nbd exists.
nbd = xopen(device, O_RDWR);
// Repeat until spanked
for (;;) {
int ro;
// Find and connect to server
sock = create_and_connect_stream_or_die(host, xatou16(port));
setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, &const_int_1,
sizeof(const_int_1));
// Log on to the server.
xread(sock, &nbd_header, 8+8+8+4 + 124);
if (memcmp(&nbd_header.magic1,
"NBDMAGIC""\x00\x00\x42\x02\x81\x86\x12\x53", 16) != 0) {
bb_error_msg_and_die("login failed");
}
// Set 4k block size. Everything uses that these days.
ioctl(nbd, NBD_SET_BLKSIZE, 4096);
ioctl(nbd, NBD_SET_SIZE_BLOCKS,
SWAP_BE64(nbd_header.devsize)/4096);
ioctl(nbd, NBD_CLEAR_SOCK);
// If the sucker was exported read only, respect that locally.
ro = (nbd_header.flags & SWAP_BE32(2)) / SWAP_BE32(2);
if (ioctl(nbd, BLKROSET, &ro) < 0) {
bb_error_msg_and_die("login failed");
}
if (timeout)
if (ioctl(nbd, NBD_SET_TIMEOUT, timeout))
bb_perror_msg_and_die("NBD_SET_TIMEOUT");
if (ioctl(nbd, NBD_SET_SOCK, sock))
bb_perror_msg_and_die("NBD_SET_SOCK");
// if (swap) mlockall(MCL_CURRENT|MCL_FUTURE);
// Open the device to force reread of the partition table.
if (!fork()) {
char *s = strrchr(device, '/');
sprintf(nbd_header.data, "/sys/block/%.32s/pid", s ?
s+1 : device);
// Is it up yet?
for (;;) {
int fd = open(nbd_header.data, O_RDONLY);
if (fd >= 0) {
close(fd);
break;
}
sleep(1);
}
open(device, O_RDONLY);
return 0;
}
// Daemonize here.
daemon(0, 0);
// Process NBD requests until further notice.
if (ioctl(nbd, NBD_DO_IT) >= 0 || errno == EBADR)
break;
close(sock);
close(nbd);
}
// Flush queue and exit.
ioctl(nbd, NBD_CLEAR_QUEUE);
ioctl(nbd, NBD_CLEAR_SOCK);
return 0;
}
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