/*
 * Copyright 2010 Rob Landley <rob@landley.net>
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config NBDCLIENT
//config:       bool "nbd-client (4.6 kb)"
//config:       default y
//config:       help
//config:       Network block device client

//applet:IF_NBDCLIENT(APPLET_NOEXEC(nbd-client, nbdclient, BB_DIR_USR_SBIN, BB_SUID_DROP, nbdclient))

//kbuild:lib-$(CONFIG_NBDCLIENT) += nbd-client.o

#include "libbb.h"
#include <netinet/tcp.h>
#include <linux/fs.h>

#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 -
//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 UNUSED_PARAM, char **argv)
{
        unsigned long timeout = 0;
#if BB_MMU
        int nofork = 0;
#endif
        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;

        BUILD_BUG_ON(offsetof(struct nbd_header_t, data) != 8+8+8+4);

        // Parse command line stuff (just a stub now)
        if (!argv[1] || !argv[2] || !argv[3] || argv[4])
                bb_show_usage();

#if !BB_MMU
        bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
#endif

        host = argv[1];
        port = argv[2];
        device = argv[3];

        // Repeat until spanked (-persist behavior)
        for (;;) {
                int sock, nbd;
                int ro;

                // Make sure the /dev/nbd exists
                nbd = xopen(device, O_RDWR);

                // Find and connect to server
                sock = create_and_connect_stream_or_die(host, xatou16(port));
                setsockopt_1(sock, IPPROTO_TCP, TCP_NODELAY);

                // 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_perror_msg_and_die("BLKROSET");

                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);

#if BB_MMU
                // Open the device to force reread of the partition table.
                // Need to do it in a separate process, since open(device)
                // needs some other process to sit in ioctl(nbd, NBD_DO_IT).
                if (fork() == 0) {
                        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
                if (!nofork) {
                        daemon(0, 0);
                        nofork = 1;
                }
#endif

                // This turns us (the process that calls this ioctl)
                // into a dedicated NBD request handler.
                // We block here for a long time.
                // When exactly ioctl returns? On a signal,
                // or if someone does ioctl(NBD_DISCONNECT) [nbd-client -d].
                if (ioctl(nbd, NBD_DO_IT) >= 0 || errno == EBADR) {
                        // Flush queue and exit
                        ioctl(nbd, NBD_CLEAR_QUEUE);
                        ioctl(nbd, NBD_CLEAR_SOCK);
                        break;
                }

                close(sock);
                close(nbd);
        }

        return 0;
}