commands: remove stack allocations

[mirror_lxc.git] / src / lxc / commands.c

/*
 * lxc: linux Container library
 *
 * (C) Copyright IBM Corp. 2007, 2009
 *
 * Authors:
 * Daniel Lezcano <daniel.lezcano at free.fr>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include <caps.h>
#include <errno.h>
#include <fcntl.h>
#include <malloc.h>
#include <poll.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

#include "af_unix.h"
#include "cgroup.h"
#include "commands.h"
#include "commands_utils.h"
#include "conf.h"
#include "config.h"
#include "confile.h"
#include "log.h"
#include "lxc.h"
#include "lxclock.h"
#include "mainloop.h"
#include "memory_utils.h"
#include "monitor.h"
#include "start.h"
#include "terminal.h"
#include "utils.h"

/*
 * This file provides the different functions for clients to query/command the
 * server. The client is typically some lxc tool and the server is typically the
 * container (ie. lxc-start).
 *
 * Each command is transactional, the clients send a request to the server and
 * the server answers the request with a message giving the request's status
 * (zero or a negative errno value). Both the request and response may contain
 * additional data.
 *
 * Each command is wrapped in a ancillary message in order to pass a credential
 * making possible to the server to check if the client is allowed to ask for
 * this command or not.
 *
 * IMPORTANTLY: Note that semantics for current commands are fixed. If you wish
 * to make any changes to how, say, LXC_CMD_GET_CONFIG_ITEM works by adding
 * information to the end of cmd.data, then you must introduce a new
 * LXC_CMD_GET_CONFIG_ITEM_V2 define with a new number. You may wish to also
 * mark LXC_CMD_GET_CONFIG_ITEM deprecated in commands.h.
 *
 * This is necessary in order to avoid having a newly compiled lxc command
 * communicating with a running (old) monitor from crashing the running
 * container.
 */

lxc_log_define(commands, lxc);

static const char *lxc_cmd_str(lxc_cmd_t cmd)
{
        static const char *const cmdname[LXC_CMD_MAX] = {
                [LXC_CMD_CONSOLE]             = "console",
                [LXC_CMD_TERMINAL_WINCH]      = "terminal_winch",
                [LXC_CMD_STOP]                = "stop",
                [LXC_CMD_GET_STATE]           = "get_state",
                [LXC_CMD_GET_INIT_PID]        = "get_init_pid",
                [LXC_CMD_GET_CLONE_FLAGS]     = "get_clone_flags",
                [LXC_CMD_GET_CGROUP]          = "get_cgroup",
                [LXC_CMD_GET_CONFIG_ITEM]     = "get_config_item",
                [LXC_CMD_GET_NAME]            = "get_name",
                [LXC_CMD_GET_LXCPATH]         = "get_lxcpath",
                [LXC_CMD_ADD_STATE_CLIENT]    = "add_state_client",
                [LXC_CMD_CONSOLE_LOG]         = "console_log",
                [LXC_CMD_SERVE_STATE_CLIENTS] = "serve_state_clients",
        };

        if (cmd >= LXC_CMD_MAX)
                return "Invalid request";

        return cmdname[cmd];
}

/*
 * lxc_cmd_rsp_recv: Receive a response to a command
 *
 * @sock  : the socket connected to the container
 * @cmd   : command to put response in
 *
 * Returns the size of the response message or < 0 on failure
 *
 * Note that if the command response datalen > 0, then data is
 * a malloc()ed buffer and should be free()ed by the caller. If
 * the response data is <= a void * worth of data, it will be
 * stored directly in data and datalen will be 0.
 *
 * As a special case, the response for LXC_CMD_CONSOLE is created
 * here as it contains an fd for the master pty passed through the
 * unix socket.
 */
static int lxc_cmd_rsp_recv(int sock, struct lxc_cmd_rr *cmd)
{
        int ret, rspfd;
        struct lxc_cmd_rsp *rsp = &cmd->rsp;

        ret = lxc_abstract_unix_recv_fds(sock, &rspfd, 1, rsp, sizeof(*rsp));
        if (ret < 0) {
                SYSWARN("Failed to receive response for command \"%s\"",
                        lxc_cmd_str(cmd->req.cmd));

                if (errno == ECONNRESET)
                        return -1;

                return -1;
        }
        TRACE("Command \"%s\" received response", lxc_cmd_str(cmd->req.cmd));

        if (cmd->req.cmd == LXC_CMD_CONSOLE) {
                struct lxc_cmd_console_rsp_data *rspdata;

                /* recv() returns 0 bytes when a tty cannot be allocated,
                 * rsp->ret is < 0 when the peer permission check failed
                 */
                if (ret == 0 || rsp->ret < 0)
                        return 0;

                rspdata = malloc(sizeof(*rspdata));
                if (!rspdata) {
                        errno = ENOMEM;
                        ERROR("Failed to allocate response buffer for command \"%s\"",
                              lxc_cmd_str(cmd->req.cmd));
                        return -1;
                }

                rspdata->masterfd = rspfd;
                rspdata->ttynum = PTR_TO_INT(rsp->data);
                rsp->data = rspdata;
        }

        if (rsp->datalen == 0) {
                DEBUG("Response data length for command \"%s\" is 0",
                      lxc_cmd_str(cmd->req.cmd));
                return ret;
        }

        if ((rsp->datalen > LXC_CMD_DATA_MAX) &&
            (cmd->req.cmd != LXC_CMD_CONSOLE_LOG)) {
                ERROR("Response data for command \"%s\" is too long: %d bytes > %d",
                      lxc_cmd_str(cmd->req.cmd), rsp->datalen, LXC_CMD_DATA_MAX);
                return -1;
        }

        if (cmd->req.cmd == LXC_CMD_CONSOLE_LOG) {
                rsp->data = malloc(rsp->datalen + 1);
                ((char *)rsp->data)[rsp->datalen] = '\0';
        } else {
                rsp->data = malloc(rsp->datalen);
        }
        if (!rsp->data) {
                errno = ENOMEM;
                ERROR("Failed to allocate response buffer for command \"%s\"",
                      lxc_cmd_str(cmd->req.cmd));
                return -1;
        }

        ret = lxc_recv_nointr(sock, rsp->data, rsp->datalen, 0);
        if (ret != rsp->datalen) {
                SYSERROR("Failed to receive response data for command \"%s\"",
                         lxc_cmd_str(cmd->req.cmd));
                return -1;
        }

        return ret;
}

/*
 * lxc_cmd_rsp_send: Send a command response
 *
 * @fd   : file descriptor of socket to send response on
 * @rsp  : response to send
 *
 * Returns 0 on success, < 0 on failure
 */
static int lxc_cmd_rsp_send(int fd, struct lxc_cmd_rsp *rsp)
{
        ssize_t ret;

        errno = EMSGSIZE;
        ret = lxc_send_nointr(fd, rsp, sizeof(*rsp), MSG_NOSIGNAL);
        if (ret < 0 || (size_t)ret != sizeof(*rsp)) {
                SYSERROR("Failed to send command response %zd", ret);
                return -1;
        }

        if (!rsp->data || rsp->datalen <= 0)
                return 0;

        errno = EMSGSIZE;
        ret = lxc_send_nointr(fd, rsp->data, rsp->datalen, MSG_NOSIGNAL);
        if (ret < 0 || ret != (ssize_t)rsp->datalen) {
                SYSWARN("Failed to send command response data %zd", ret);
                return -1;
        }

        return 0;
}

static int lxc_cmd_send(const char *name, struct lxc_cmd_rr *cmd,
                        const char *lxcpath, const char *hashed_sock_name)
{
        int client_fd, saved_errno;
        ssize_t ret = -1;

        client_fd = lxc_cmd_connect(name, lxcpath, hashed_sock_name, "command");
        if (client_fd < 0)
                return -1;

        ret = lxc_abstract_unix_send_credential(client_fd, &cmd->req,
                                                sizeof(cmd->req));
        if (ret < 0 || (size_t)ret != sizeof(cmd->req))
                goto on_error;

        if (cmd->req.datalen <= 0)
                return client_fd;

        errno = EMSGSIZE;
        ret = lxc_send_nointr(client_fd, (void *)cmd->req.data,
                              cmd->req.datalen, MSG_NOSIGNAL);
        if (ret < 0 || ret != (ssize_t)cmd->req.datalen)
                goto on_error;

        return client_fd;

on_error:
        saved_errno = errno;
        close(client_fd);
        errno = saved_errno;

        return -1;
}

/*
 * lxc_cmd: Connect to the specified running container, send it a command
 * request and collect the response
 *
 * @name           : name of container to connect to
 * @cmd            : command with initialized request to send
 * @stopped        : output indicator if the container was not running
 * @lxcpath        : the lxcpath in which the container is running
 *
 * Returns the size of the response message on success, < 0 on failure
 *
 * Note that there is a special case for LXC_CMD_CONSOLE. For this command
 * the fd cannot be closed because it is used as a placeholder to indicate
 * that a particular tty slot is in use. The fd is also used as a signal to
 * the container that when the caller dies or closes the fd, the container
 * will notice the fd on its side of the socket in its mainloop select and
 * then free the slot with lxc_cmd_fd_cleanup(). The socket fd will be
 * returned in the cmd response structure.
 */
static int lxc_cmd(const char *name, struct lxc_cmd_rr *cmd, int *stopped,
                   const char *lxcpath, const char *hashed_sock_name)
{
        int client_fd, saved_errno;
        int ret = -1;
        bool stay_connected = false;

        if (cmd->req.cmd == LXC_CMD_CONSOLE ||
            cmd->req.cmd == LXC_CMD_ADD_STATE_CLIENT)
                stay_connected = true;

        *stopped = 0;

        client_fd = lxc_cmd_send(name, cmd, lxcpath, hashed_sock_name);
        if (client_fd < 0) {
                SYSTRACE("Command \"%s\" failed to connect command socket",
                         lxc_cmd_str(cmd->req.cmd));

                if (errno == ECONNREFUSED || errno == EPIPE)
                        *stopped = 1;

                return -1;
        }

        ret = lxc_cmd_rsp_recv(client_fd, cmd);
        if (ret < 0 && errno == ECONNRESET)
                *stopped = 1;

        if (!stay_connected || ret <= 0) {
                saved_errno = errno;
                close(client_fd);
                errno = saved_errno;
                return ret;
        }

        if (stay_connected && ret > 0)
                cmd->rsp.ret = client_fd;

        return ret;
}

int lxc_try_cmd(const char *name, const char *lxcpath)
{
        int stopped, ret;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_GET_INIT_PID },
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (stopped)
                return 0;
        if (ret > 0 && cmd.rsp.ret < 0) {
                errno = cmd.rsp.ret;
                return -1;
        }
        if (ret > 0)
                return 0;

        /* At this point we weren't denied access, and the container *was*
         * started. There was some inexplicable error in the protocol.  I'm not
         * clear on whether we should return -1 here, but we didn't receive a
         * -EACCES, so technically it's not that we're not allowed to control
         * the container - it's just not behaving.
         */
        return 0;
}

/* Implementations of the commands and their callbacks */

/*
 * lxc_cmd_get_init_pid: Get pid of the container's init process
 *
 * @name      : name of container to connect to
 * @lxcpath   : the lxcpath in which the container is running
 *
 * Returns the pid on success, < 0 on failure
 */
pid_t lxc_cmd_get_init_pid(const char *name, const char *lxcpath)
{
        int ret, stopped;
        intmax_t pid;
        struct lxc_cmd_rr cmd = {
                .req = {
                        .cmd = LXC_CMD_GET_INIT_PID
                },
                .rsp = {
                        .data = INTMAX_TO_PTR((intmax_t){-1})
                }
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0)
                return -1;

        pid = PTR_TO_INTMAX(cmd.rsp.data);
        if (pid < 0)
                return -1;

        /* We need to assume that pid_t can actually hold any pid given to us
         * by the kernel. If it can't it's a libc bug.
         */
        return (pid_t)pid;
}

static int lxc_cmd_get_init_pid_callback(int fd, struct lxc_cmd_req *req,
                                         struct lxc_handler *handler)
{
        intmax_t pid = handler->pid;

        struct lxc_cmd_rsp rsp = {
                .data = INTMAX_TO_PTR(pid)
        };

        return lxc_cmd_rsp_send(fd, &rsp);
}

/*
 * lxc_cmd_get_clone_flags: Get clone flags container was spawned with
 *
 * @name      : name of container to connect to
 * @lxcpath   : the lxcpath in which the container is running
 *
 * Returns the clone flags on success, < 0 on failure
 */
int lxc_cmd_get_clone_flags(const char *name, const char *lxcpath)
{
        int ret, stopped;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_GET_CLONE_FLAGS },
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0)
                return ret;

        return PTR_TO_INT(cmd.rsp.data);
}

static int lxc_cmd_get_clone_flags_callback(int fd, struct lxc_cmd_req *req,
                                            struct lxc_handler *handler)
{
        struct lxc_cmd_rsp rsp = { .data = INT_TO_PTR(handler->ns_clone_flags) };

        return lxc_cmd_rsp_send(fd, &rsp);
}

/*
 * lxc_cmd_get_cgroup_path: Calculate a container's cgroup path for a
 * particular subsystem. This is the cgroup path relative to the root
 * of the cgroup filesystem.
 *
 * @name      : name of container to connect to
 * @lxcpath   : the lxcpath in which the container is running
 * @subsystem : the subsystem being asked about
 *
 * Returns the path on success, NULL on failure. The caller must free() the
 * returned path.
 */
char *lxc_cmd_get_cgroup_path(const char *name, const char *lxcpath,
                              const char *subsystem)
{
        int ret, stopped;
        struct lxc_cmd_rr cmd = {
                .req = {
                        .cmd = LXC_CMD_GET_CGROUP,
                        .data = subsystem,
                        .datalen = 0,
                },
        };

        cmd.req.data = subsystem;
        cmd.req.datalen = 0;
        if (subsystem)
                cmd.req.datalen = strlen(subsystem) + 1;

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0)
                return NULL;

        if (ret == 0)
                return NULL;

        if (cmd.rsp.ret < 0 || cmd.rsp.datalen < 0)
                return NULL;

        return cmd.rsp.data;
}

static int lxc_cmd_get_cgroup_callback(int fd, struct lxc_cmd_req *req,
                                       struct lxc_handler *handler)
{
        const char *path;
        struct lxc_cmd_rsp rsp;
        struct cgroup_ops *cgroup_ops = handler->cgroup_ops;

        if (req->datalen > 0)
                path = cgroup_ops->get_cgroup(cgroup_ops, req->data);
        else
                path = cgroup_ops->get_cgroup(cgroup_ops, NULL);
        if (!path)
                return -1;

        rsp.ret = 0;
        rsp.datalen = strlen(path) + 1;
        rsp.data = (char *)path;

        return lxc_cmd_rsp_send(fd, &rsp);
}

/*
 * lxc_cmd_get_config_item: Get config item the running container
 *
 * @name     : name of container to connect to
 * @item     : the configuration item to retrieve (ex: lxc.net.0.veth.pair)
 * @lxcpath  : the lxcpath in which the container is running
 *
 * Returns the item on success, NULL on failure. The caller must free() the
 * returned item.
 */
char *lxc_cmd_get_config_item(const char *name, const char *item,
                              const char *lxcpath)
{
        int ret, stopped;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_GET_CONFIG_ITEM,
                         .data = item,
                         .datalen = strlen(item) + 1,
                       },
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0)
                return NULL;

        if (cmd.rsp.ret == 0)
                return cmd.rsp.data;

        return NULL;
}

static int lxc_cmd_get_config_item_callback(int fd, struct lxc_cmd_req *req,
                                            struct lxc_handler *handler)
{
        __do_free char *cidata = NULL;
        int cilen;
        struct lxc_config_t *item;
        struct lxc_cmd_rsp rsp;

        memset(&rsp, 0, sizeof(rsp));
        item = lxc_get_config(req->data);
        if (!item)
                goto err1;

        cilen = item->get(req->data, NULL, 0, handler->conf, NULL);
        if (cilen <= 0)
                goto err1;

        cidata = must_realloc(NULL, cilen + 1);
        if (item->get(req->data, cidata, cilen + 1, handler->conf, NULL) != cilen)
                goto err1;

        cidata[cilen] = '\0';
        rsp.data = cidata;
        rsp.datalen = cilen + 1;
        rsp.ret = 0;
        goto out;

err1:
        rsp.ret = -1;
out:
        return lxc_cmd_rsp_send(fd, &rsp);
}

/*
 * lxc_cmd_get_state: Get current state of the container
 *
 * @name      : name of container to connect to
 * @lxcpath   : the lxcpath in which the container is running
 *
 * Returns the state on success, < 0 on failure
 */
int lxc_cmd_get_state(const char *name, const char *lxcpath)
{
        int ret, stopped;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_GET_STATE }
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0 && stopped)
                return STOPPED;

        if (ret < 0)
                return -1;

        if (!ret) {
                WARN("Container \"%s\" has stopped before sending its state", name);
                return -1;
        }

        DEBUG("Container \"%s\" is in \"%s\" state", name,
              lxc_state2str(PTR_TO_INT(cmd.rsp.data)));

        return PTR_TO_INT(cmd.rsp.data);
}

static int lxc_cmd_get_state_callback(int fd, struct lxc_cmd_req *req,
                                      struct lxc_handler *handler)
{
        struct lxc_cmd_rsp rsp = { .data = INT_TO_PTR(handler->state) };

        return lxc_cmd_rsp_send(fd, &rsp);
}

/*
 * lxc_cmd_stop: Stop the container previously started with lxc_start. All
 * the processes running inside this container will be killed.
 *
 * @name     : name of container to connect to
 * @lxcpath  : the lxcpath in which the container is running
 *
 * Returns 0 on success, < 0 on failure
 */
int lxc_cmd_stop(const char *name, const char *lxcpath)
{
        int ret, stopped;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_STOP },
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0) {
                if (stopped) {
                        INFO("Container \"%s\" is already stopped", name);
                        return 0;
                }

                return -1;
        }

        /* We do not expect any answer, because we wait for the connection to be
         * closed.
         */
        if (ret > 0) {
                errno = -cmd.rsp.ret;
                SYSERROR("Failed to stop container \"%s\"", name);
                return -1;
        }

        INFO("Container \"%s\" has stopped", name);
        return 0;
}

static int lxc_cmd_stop_callback(int fd, struct lxc_cmd_req *req,
                                 struct lxc_handler *handler)
{
        struct lxc_cmd_rsp rsp;
        int stopsignal = SIGKILL;
        struct cgroup_ops *cgroup_ops = handler->cgroup_ops;

        if (handler->conf->stopsignal)
                stopsignal = handler->conf->stopsignal;
        memset(&rsp, 0, sizeof(rsp));
        rsp.ret = kill(handler->pid, stopsignal);
        if (!rsp.ret) {
                /* We can't just use lxc_unfreeze() since we are already in the
                 * context of handling the STOP cmd in lxc-start, and calling
                 * lxc_unfreeze() would do another cmd (GET_CGROUP) which would
                 * deadlock us.
                 */
                if (!cgroup_ops->get_cgroup(cgroup_ops, "freezer"))
                        return 0;

                if (cgroup_ops->unfreeze(cgroup_ops))
                        return 0;

                ERROR("Failed to unfreeze container \"%s\"", handler->name);
                rsp.ret = -1;
        }

        return lxc_cmd_rsp_send(fd, &rsp);
}

/*
 * lxc_cmd_terminal_winch: noop
 *
 * @name      : name of container to connect to
 * @lxcpath   : the lxcpath in which the container is running
 *
 * Returns 0 on success, < 0 on failure
 */
int lxc_cmd_terminal_winch(const char *name, const char *lxcpath)
{
        return 0;
}

static int lxc_cmd_terminal_winch_callback(int fd, struct lxc_cmd_req *req,
                                           struct lxc_handler *handler)
{
        /* should never be called */
        return -1;
}

/*
 * lxc_cmd_console: Open an fd to a tty in the container
 *
 * @name           : name of container to connect to
 * @ttynum         : in:  the tty to open or -1 for next available
 *                 : out: the tty allocated
 * @fd             : out: file descriptor for master side of pty
 * @lxcpath        : the lxcpath in which the container is running
 *
 * Returns fd holding tty allocated on success, < 0 on failure
 */
int lxc_cmd_console(const char *name, int *ttynum, int *fd, const char *lxcpath)
{
        int ret, stopped;
        struct lxc_cmd_console_rsp_data *rspdata;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_CONSOLE, .data = INT_TO_PTR(*ttynum) },
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0)
                return ret;

        if (cmd.rsp.ret < 0) {
                errno = -cmd.rsp.ret;
                SYSERROR("Denied access to tty");
                ret = -1;
                goto out;
        }

        if (ret == 0) {
                ERROR("tty number %d invalid, busy or all ttys busy", *ttynum);
                ret = -1;
                goto out;
        }

        rspdata = cmd.rsp.data;
        if (rspdata->masterfd < 0) {
                ERROR("Unable to allocate fd for tty %d", rspdata->ttynum);
                goto out;
        }

        ret = cmd.rsp.ret; /* socket fd */
        *fd = rspdata->masterfd;
        *ttynum = rspdata->ttynum;
        INFO("Alloced fd %d for tty %d via socket %d", *fd, rspdata->ttynum, ret);

out:
        free(cmd.rsp.data);
        return ret;
}

static int lxc_cmd_console_callback(int fd, struct lxc_cmd_req *req,
                                    struct lxc_handler *handler)
{
        int masterfd, ret;
        struct lxc_cmd_rsp rsp;
        int ttynum = PTR_TO_INT(req->data);

        masterfd = lxc_terminal_allocate(handler->conf, fd, &ttynum);
        if (masterfd < 0)
                goto out_close;

        memset(&rsp, 0, sizeof(rsp));
        rsp.data = INT_TO_PTR(ttynum);
        ret = lxc_abstract_unix_send_fds(fd, &masterfd, 1, &rsp, sizeof(rsp));
        if (ret < 0) {
                SYSERROR("Failed to send tty to client");
                lxc_terminal_free(handler->conf, fd);
                goto out_close;
        }

        return 0;

out_close:
        /* Special indicator to lxc_cmd_handler() to close the fd and do
         * related cleanup.
         */
        return 1;
}

/*
 * lxc_cmd_get_name: Returns the name of the container
 *
 * @hashed_sock_name: hashed socket name
 *
 * Returns the name on success, NULL on failure.
 */
char *lxc_cmd_get_name(const char *hashed_sock_name)
{
        int ret, stopped;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_GET_NAME},
        };

        ret = lxc_cmd(NULL, &cmd, &stopped, NULL, hashed_sock_name);
        if (ret < 0)
                return NULL;

        if (cmd.rsp.ret == 0)
                return cmd.rsp.data;

        return NULL;
}

static int lxc_cmd_get_name_callback(int fd, struct lxc_cmd_req *req,
                                     struct lxc_handler *handler)
{
        struct lxc_cmd_rsp rsp;

        memset(&rsp, 0, sizeof(rsp));

        rsp.data = (char *)handler->name;
        rsp.datalen = strlen(handler->name) + 1;
        rsp.ret = 0;

        return lxc_cmd_rsp_send(fd, &rsp);
}

/*
 * lxc_cmd_get_lxcpath: Returns the lxcpath of the container
 *
 * @hashed_sock_name: hashed socket name
 *
 * Returns the lxcpath on success, NULL on failure.
 */
char *lxc_cmd_get_lxcpath(const char *hashed_sock_name)
{
        int ret, stopped;
        struct lxc_cmd_rr cmd = {
                .req = { .cmd = LXC_CMD_GET_LXCPATH},
        };

        ret = lxc_cmd(NULL, &cmd, &stopped, NULL, hashed_sock_name);
        if (ret < 0)
                return NULL;

        if (cmd.rsp.ret == 0)
                return cmd.rsp.data;

        return NULL;
}

static int lxc_cmd_get_lxcpath_callback(int fd, struct lxc_cmd_req *req,
                                        struct lxc_handler *handler)
{
        struct lxc_cmd_rsp rsp;

        memset(&rsp, 0, sizeof(rsp));

        rsp.ret = 0;
        rsp.data = (char *)handler->lxcpath;
        rsp.datalen = strlen(handler->lxcpath) + 1;

        return lxc_cmd_rsp_send(fd, &rsp);
}

int lxc_cmd_add_state_client(const char *name, const char *lxcpath,
                             lxc_state_t states[MAX_STATE],
                             int *state_client_fd)
{
        int state, stopped;
        ssize_t ret;
        struct lxc_cmd_rr cmd = {
            .req = {
                .cmd     = LXC_CMD_ADD_STATE_CLIENT,
                .data    = states,
                .datalen = (sizeof(lxc_state_t) * MAX_STATE)
            },
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (states[STOPPED] != 0 && stopped != 0)
                return STOPPED;

        if (ret < 0) {
                if (errno != ECONNREFUSED)
                        SYSERROR("Failed to execute command");

                return -1;
        }

        /* We should now be guaranteed to get an answer from the state sending
         * function.
         */
        if (cmd.rsp.ret < 0) {
                errno = -cmd.rsp.ret;
                SYSERROR("Failed to receive socket fd");
                return -1;
        }

        state = PTR_TO_INT(cmd.rsp.data);
        if (state < MAX_STATE) {
                TRACE("Container is already in requested state %s", lxc_state2str(state));
                close(cmd.rsp.ret);
                return state;
        }

        *state_client_fd = cmd.rsp.ret;
        TRACE("Added state client %d to state client list", cmd.rsp.ret);
        return MAX_STATE;
}

static int lxc_cmd_add_state_client_callback(int fd, struct lxc_cmd_req *req,
                                             struct lxc_handler *handler)
{
        int ret;
        struct lxc_cmd_rsp rsp = {0};

        if (req->datalen < 0)
                goto reap_client_fd;

        if (req->datalen != (sizeof(lxc_state_t) * MAX_STATE))
                goto reap_client_fd;

        if (!req->data)
                goto reap_client_fd;

        rsp.ret = lxc_add_state_client(fd, handler, (lxc_state_t *)req->data);
        if (rsp.ret < 0)
                goto reap_client_fd;

        rsp.data = INT_TO_PTR(rsp.ret);

        ret = lxc_cmd_rsp_send(fd, &rsp);
        if (ret < 0)
                goto reap_client_fd;

        return 0;

reap_client_fd:
        /* Special indicator to lxc_cmd_handler() to close the fd and do related
         * cleanup.
         */
        return 1;
}

int lxc_cmd_console_log(const char *name, const char *lxcpath,
                        struct lxc_console_log *log)
{
        int ret, stopped;
        struct lxc_cmd_console_log data;
        struct lxc_cmd_rr cmd;

        data.clear = log->clear;
        data.read = log->read;
        data.read_max = *log->read_max;

        cmd.req.cmd = LXC_CMD_CONSOLE_LOG;
        cmd.req.data = &data;
        cmd.req.datalen = sizeof(struct lxc_cmd_console_log);

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0)
                return ret;

        /* There is nothing to be read from the buffer. So clear any values we
         * where passed to clearly indicate to the user that nothing went wrong.
         */
        if (cmd.rsp.ret == -ENODATA || cmd.rsp.ret == -EFAULT || cmd.rsp.ret == -ENOENT) {
                *log->read_max = 0;
                log->data = NULL;
        }

        /* This is a proper error so don't touch any values we were passed. */
        if (cmd.rsp.ret < 0)
                return cmd.rsp.ret;

        *log->read_max = cmd.rsp.datalen;
        log->data = cmd.rsp.data;

        return 0;
}

static int lxc_cmd_console_log_callback(int fd, struct lxc_cmd_req *req,
                                        struct lxc_handler *handler)
{
        struct lxc_cmd_rsp rsp;
        uint64_t buffer_size = handler->conf->console.buffer_size;
        const struct lxc_cmd_console_log *log = req->data;
        struct lxc_ringbuf *buf = &handler->conf->console.ringbuf;

        rsp.ret = -EFAULT;
        rsp.datalen = 0;
        rsp.data = NULL;
        if (buffer_size <= 0)
                goto out;

        if (log->read || log->write_logfile)
                rsp.datalen = lxc_ringbuf_used(buf);

        if (log->read)
                rsp.data = lxc_ringbuf_get_read_addr(buf);

        if (log->read_max > 0 && (log->read_max <= rsp.datalen))
                rsp.datalen = log->read_max;

        /* there's nothing to read */
        rsp.ret = -ENODATA;
        if (log->read && (buf->r_off == buf->w_off))
                goto out;

        rsp.ret = 0;
        if (log->clear)
                lxc_ringbuf_clear(buf); /* clear the ringbuffer */
        else if (rsp.datalen > 0)
                lxc_ringbuf_move_read_addr(buf, rsp.datalen);

out:
        return lxc_cmd_rsp_send(fd, &rsp);
}

int lxc_cmd_serve_state_clients(const char *name, const char *lxcpath,
                                lxc_state_t state)
{
        int stopped;
        ssize_t ret;
        struct lxc_cmd_rr cmd = {
            .req = {
                .cmd  = LXC_CMD_SERVE_STATE_CLIENTS,
                .data = INT_TO_PTR(state)
            },
        };

        ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
        if (ret < 0) {
                SYSERROR("Failed to execute command");
                return -1;
        }

        return 0;
}

static int lxc_cmd_serve_state_clients_callback(int fd, struct lxc_cmd_req *req,
                                                struct lxc_handler *handler)
{
        int ret;
        lxc_state_t state = PTR_TO_INT(req->data);
        struct lxc_cmd_rsp rsp = {0};

        ret = lxc_serve_state_clients(handler->name, handler, state);
        if (ret < 0)
                goto reap_client_fd;

        ret = lxc_cmd_rsp_send(fd, &rsp);
        if (ret < 0)
                goto reap_client_fd;

        return 0;

reap_client_fd:
        /* Special indicator to lxc_cmd_handler() to close the fd and do related
         * cleanup.
         */
        return 1;
}

static int lxc_cmd_process(int fd, struct lxc_cmd_req *req,
                           struct lxc_handler *handler)
{
        typedef int (*callback)(int, struct lxc_cmd_req *, struct lxc_handler *);

        callback cb[LXC_CMD_MAX] = {
                [LXC_CMD_CONSOLE]             = lxc_cmd_console_callback,
                [LXC_CMD_TERMINAL_WINCH]      = lxc_cmd_terminal_winch_callback,
                [LXC_CMD_STOP]                = lxc_cmd_stop_callback,
                [LXC_CMD_GET_STATE]           = lxc_cmd_get_state_callback,
                [LXC_CMD_GET_INIT_PID]        = lxc_cmd_get_init_pid_callback,
                [LXC_CMD_GET_CLONE_FLAGS]     = lxc_cmd_get_clone_flags_callback,
                [LXC_CMD_GET_CGROUP]          = lxc_cmd_get_cgroup_callback,
                [LXC_CMD_GET_CONFIG_ITEM]     = lxc_cmd_get_config_item_callback,
                [LXC_CMD_GET_NAME]            = lxc_cmd_get_name_callback,
                [LXC_CMD_GET_LXCPATH]         = lxc_cmd_get_lxcpath_callback,
                [LXC_CMD_ADD_STATE_CLIENT]    = lxc_cmd_add_state_client_callback,
                [LXC_CMD_CONSOLE_LOG]         = lxc_cmd_console_log_callback,
                [LXC_CMD_SERVE_STATE_CLIENTS] = lxc_cmd_serve_state_clients_callback,
        };

        if (req->cmd >= LXC_CMD_MAX) {
                ERROR("Undefined command id %d", req->cmd);
                return -1;
        }
        return cb[req->cmd](fd, req, handler);
}

static void lxc_cmd_fd_cleanup(int fd, struct lxc_handler *handler,
                               struct lxc_epoll_descr *descr,
                               const lxc_cmd_t cmd)
{
        struct lxc_state_client *client;
        struct lxc_list *cur, *next;

        lxc_terminal_free(handler->conf, fd);
        lxc_mainloop_del_handler(descr, fd);
        if (cmd != LXC_CMD_ADD_STATE_CLIENT) {
                close(fd);
                return;
        }

        lxc_list_for_each_safe(cur, &handler->conf->state_clients, next) {
                client = cur->elem;
                if (client->clientfd != fd)
                        continue;

                /* kick client from list */
                lxc_list_del(cur);
                close(client->clientfd);
                free(cur->elem);
                free(cur);
                /* No need to walk the whole list. If we found the state client
                 * fd there can't be a second one.
                 */
                break;
        }
}

static int lxc_cmd_handler(int fd, uint32_t events, void *data,
                           struct lxc_epoll_descr *descr)
{
        __do_free void *reqdata = NULL;
        int ret;
        struct lxc_cmd_req req;
        struct lxc_handler *handler = data;

        ret = lxc_abstract_unix_rcv_credential(fd, &req, sizeof(req));
        if (ret < 0) {
                SYSERROR("Failed to receive data on command socket for command "
                         "\"%s\"", lxc_cmd_str(req.cmd));

                if (errno == EACCES) {
                        /* We don't care for the peer, just send and close. */
                        struct lxc_cmd_rsp rsp = {.ret = ret};

                        lxc_cmd_rsp_send(fd, &rsp);
                }

                goto out_close;
        }

        if (ret == 0)
                goto out_close;

        if (ret != sizeof(req)) {
                WARN("Failed to receive full command request. Ignoring request "
                     "for \"%s\"", lxc_cmd_str(req.cmd));
                ret = -1;
                goto out_close;
        }

        if ((req.datalen > LXC_CMD_DATA_MAX) &&
            (req.cmd != LXC_CMD_CONSOLE_LOG)) {
                ERROR("Received command data length %d is too large for "
                      "command \"%s\"", req.datalen, lxc_cmd_str(req.cmd));
                errno = EFBIG;
                ret = -EFBIG;
                goto out_close;
        }

        if (req.datalen > 0) {
                reqdata = must_realloc(NULL, req.datalen);
                ret = lxc_recv_nointr(fd, reqdata, req.datalen, 0);
                if (ret != req.datalen) {
                        WARN("Failed to receive full command request. Ignoring "
                             "request for \"%s\"", lxc_cmd_str(req.cmd));
                        ret = LXC_MAINLOOP_ERROR;
                        goto out_close;
                }

                req.data = reqdata;
        }

        ret = lxc_cmd_process(fd, &req, handler);
        if (ret) {
                /* This is not an error, but only a request to close fd. */
                ret = LXC_MAINLOOP_CONTINUE;
                goto out_close;
        }

out:
        return ret;

out_close:
        lxc_cmd_fd_cleanup(fd, handler, descr, req.cmd);
        goto out;
}

static int lxc_cmd_accept(int fd, uint32_t events, void *data,
                          struct lxc_epoll_descr *descr)
{
        int connection;
        int opt = 1, ret = -1;

        connection = accept(fd, NULL, 0);
        if (connection < 0) {
                SYSERROR("Failed to accept connection to run command");
                return LXC_MAINLOOP_ERROR;
        }

        ret = fcntl(connection, F_SETFD, FD_CLOEXEC);
        if (ret < 0) {
                SYSERROR("Failed to set close-on-exec on incoming command connection");
                goto out_close;
        }

        ret = setsockopt(connection, SOL_SOCKET, SO_PASSCRED, &opt, sizeof(opt));
        if (ret < 0) {
                SYSERROR("Failed to enable necessary credentials on command socket");
                goto out_close;
        }

        ret = lxc_mainloop_add_handler(descr, connection, lxc_cmd_handler, data);
        if (ret) {
                ERROR("Failed to add command handler");
                goto out_close;
        }

out:
        return ret;

out_close:
        close(connection);
        goto out;
}

int lxc_cmd_init(const char *name, const char *lxcpath, const char *suffix)
{
        int fd, ret;
        char path[LXC_AUDS_ADDR_LEN] = {0};

        ret = lxc_make_abstract_socket_name(path, sizeof(path), name, lxcpath, NULL, suffix);
        if (ret < 0)
                return -1;
        TRACE("Creating abstract unix socket \"%s\"", &path[1]);

        fd = lxc_abstract_unix_open(path, SOCK_STREAM, 0);
        if (fd < 0) {
                SYSERROR("Failed to create command socket %s", &path[1]);
                if (errno == EADDRINUSE)
                        ERROR("Container \"%s\" appears to be already running", name);

                return -1;
        }

        ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
        if (ret < 0) {
                SYSERROR("Failed to set FD_CLOEXEC on command socket file descriptor");
                close(fd);
                return -1;
        }

        return fd;
}

int lxc_cmd_mainloop_add(const char *name, struct lxc_epoll_descr *descr,
                         struct lxc_handler *handler)
{
        int ret;
        int fd = handler->conf->maincmd_fd;

        ret = lxc_mainloop_add_handler(descr, fd, lxc_cmd_accept, handler);
        if (ret < 0) {
                ERROR("Failed to add handler for command socket");
                close(fd);
        }

        return ret;
}