umid.c

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/*
 * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <init.h>
#include <os.h>

#define UML_DIR "~/.uml/"

#define UMID_LEN 64

/* Changed by set_umid, which is run early in boot */
static char umid[UMID_LEN] = { 0 };

/* Changed by set_uml_dir and make_uml_dir, which are run early in boot */
static char *uml_dir = UML_DIR;

static int __init make_uml_dir(void)
{
    char dir[512] = { '\0' };
    int len, err;

    if (*uml_dir == '~') {
        char *home = getenv("HOME");

        err = -ENOENT;
        if (home == NULL) {
            printk(UM_KERN_ERR "make_uml_dir : no value in "
                   "environment for $HOME\n");
            goto err;
        }
        strlcpy(dir, home, sizeof(dir));
        uml_dir++;
    }
    strlcat(dir, uml_dir, sizeof(dir));
    len = strlen(dir);
    if (len > 0 && dir[len - 1] != '/')
        strlcat(dir, "/", sizeof(dir));

    err = -ENOMEM;
    uml_dir = malloc(strlen(dir) + 1);
    if (uml_dir == NULL) {
        printf("make_uml_dir : malloc failed, errno = %d\n", errno);
        goto err;
    }
    strcpy(uml_dir, dir);

    if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
            printf("Failed to mkdir '%s': %s\n", uml_dir, strerror(errno));
        err = -errno;
        goto err_free;
    }
    return 0;

err_free:
    free(uml_dir);
err:
    uml_dir = NULL;
    return err;
}

/*
 * Unlinks the files contained in @dir and then removes @dir.
 * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
 * ignore ENOENT errors for anything (they happen, strangely enough - possibly
 * due to races between multiple dying UML threads).
 */
static int remove_files_and_dir(char *dir)
{
    DIR *directory;
    struct dirent *ent;
    int len;
    char file[256];
    int ret;

    directory = opendir(dir);
    if (directory == NULL) {
        if (errno != ENOENT)
            return -errno;
        else
            return 0;
    }

    while ((ent = readdir(directory)) != NULL) {
        if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
            continue;
        len = strlen(dir) + sizeof("/") + strlen(ent->d_name) + 1;
        if (len > sizeof(file)) {
            ret = -E2BIG;
            goto out;
        }

        sprintf(file, "%s/%s", dir, ent->d_name);
        if (unlink(file) < 0 && errno != ENOENT) {
            ret = -errno;
            goto out;
        }
    }

    if (rmdir(dir) < 0 && errno != ENOENT) {
        ret = -errno;
        goto out;
    }

    ret = 0;
out:
    closedir(directory);
    return ret;
}

/*
 * This says that there isn't already a user of the specified directory even if
 * there are errors during the checking.  This is because if these errors
 * happen, the directory is unusable by the pre-existing UML, so we might as
 * well take it over.  This could happen either by
 *  the existing UML somehow corrupting its umid directory
 *  something other than UML sticking stuff in the directory
 *  this boot racing with a shutdown of the other UML
 * In any of these cases, the directory isn't useful for anything else.
 *
 * Boolean return: 1 if in use, 0 otherwise.
 */
static inline int is_umdir_used(char *dir)
{
    char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
    char pid[sizeof("nnnnn\0")], *end;
    int dead, fd, p, n, err;

    n = snprintf(file, sizeof(file), "%s/pid", dir);
    if (n >= sizeof(file)) {
        printk(UM_KERN_ERR "is_umdir_used - pid filename too long\n");
        err = -E2BIG;
        goto out;
    }

    dead = 0;
    fd = open(file, O_RDONLY);
    if (fd < 0) {
        fd = -errno;
        if (fd != -ENOENT) {
            printk(UM_KERN_ERR "is_umdir_used : couldn't open pid "
                   "file '%s', err = %d\n", file, -fd);
        }
        goto out;
    }

    err = 0;
    n = read(fd, pid, sizeof(pid));
    if (n < 0) {
        printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
               "'%s', err = %d\n", file, errno);
        goto out_close;
    } else if (n == 0) {
        printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
               "'%s', 0-byte read\n", file);
        goto out_close;
    }

    p = strtoul(pid, &end, 0);
    if (end == pid) {
        printk(UM_KERN_ERR "is_umdir_used : couldn't parse pid file "
               "'%s', errno = %d\n", file, errno);
        goto out_close;
    }

    if ((kill(p, 0) == 0) || (errno != ESRCH)) {
        printk(UM_KERN_ERR "umid \"%s\" is already in use by pid %d\n",
               umid, p);
        return 1;
    }

out_close:
    close(fd);
out:
    return 0;
}

/*
 * Try to remove the directory @dir unless it's in use.
 * Precondition: @dir exists.
 * Returns 0 for success, < 0 for failure in removal or if the directory is in
 * use.
 */
static int umdir_take_if_dead(char *dir)
{
    int ret;
    if (is_umdir_used(dir))
        return -EEXIST;

    ret = remove_files_and_dir(dir);
    if (ret) {
        printk(UM_KERN_ERR "is_umdir_used - remove_files_and_dir "
               "failed with err = %d\n", ret);
    }
    return ret;
}

static void __init create_pid_file(void)
{
    char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
    char pid[sizeof("nnnnn\0")];
    int fd, n;

    if (umid_file_name("pid", file, sizeof(file)))
        return;

    fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
    if (fd < 0) {
        printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
               "%s\n", file, strerror(errno));
        return;
    }

    snprintf(pid, sizeof(pid), "%d\n", getpid());
    n = write(fd, pid, strlen(pid));
    if (n != strlen(pid))
        printk(UM_KERN_ERR "Write of pid file failed - err = %d\n",
               errno);

    close(fd);
}

int __init set_umid(char *name)
{
    if (strlen(name) > UMID_LEN - 1)
        return -E2BIG;

    strlcpy(umid, name, sizeof(umid));

    return 0;
}

/* Changed in make_umid, which is called during early boot */
static int umid_setup = 0;

static int __init make_umid(void)
{
    int fd, err;
    char tmp[256];

    if (umid_setup)
        return 0;

    make_uml_dir();

    if (*umid == '\0') {
        strlcpy(tmp, uml_dir, sizeof(tmp));
        strlcat(tmp, "XXXXXX", sizeof(tmp));
        fd = mkstemp(tmp);
        if (fd < 0) {
            printk(UM_KERN_ERR "make_umid - mkstemp(%s) failed: "
                   "%s\n", tmp, strerror(errno));
            err = -errno;
            goto err;
        }

        close(fd);

        set_umid(&tmp[strlen(uml_dir)]);

        /*
         * There's a nice tiny little race between this unlink and
         * the mkdir below.  It'd be nice if there were a mkstemp
         * for directories.
         */
        if (unlink(tmp)) {
            err = -errno;
            goto err;
        }
    }

    snprintf(tmp, sizeof(tmp), "%s%s", uml_dir, umid);
    err = mkdir(tmp, 0777);
    if (err < 0) {
        err = -errno;
        if (err != -EEXIST)
            goto err;

        if (umdir_take_if_dead(tmp) < 0)
            goto err;

        err = mkdir(tmp, 0777);
    }
    if (err) {
        err = -errno;
        printk(UM_KERN_ERR "Failed to create '%s' - err = %d\n", umid,
               errno);
        goto err;
    }

    umid_setup = 1;

    create_pid_file();

    err = 0;
 err:
    return err;
}

static int __init make_umid_init(void)
{
    if (!make_umid())
        return 0;

    /*
     * If initializing with the given umid failed, then try again with
     * a random one.
     */
    printk(UM_KERN_ERR "Failed to initialize umid \"%s\", trying with a "
           "random umid\n", umid);
    *umid = '\0';
    make_umid();

    return 0;
}

__initcall(make_umid_init);

int __init umid_file_name(char *name, char *buf, int len)
{
    int n, err;

    err = make_umid();
    if (err)
        return err;

    n = snprintf(buf, len, "%s%s/%s", uml_dir, umid, name);
    if (n >= len) {
        printk(UM_KERN_ERR "umid_file_name : buffer too short\n");
        return -E2BIG;
    }

    return 0;
}

char *get_umid(void)
{
    return umid;
}

static int __init set_uml_dir(char *name, int *add)
{
    if (*name == '\0') {
        printf("uml_dir can't be an empty string\n");
        return 0;
    }

    if (name[strlen(name) - 1] == '/') {
        uml_dir = name;
        return 0;
    }

    uml_dir = malloc(strlen(name) + 2);
    if (uml_dir == NULL) {
        printf("Failed to malloc uml_dir - error = %d\n", errno);

        /*
         * Return 0 here because do_initcalls doesn't look at
         * the return value.
         */
        return 0;
    }
    sprintf(uml_dir, "%s/", name);

    return 0;
}

__uml_setup("uml_dir=", set_uml_dir,
"uml_dir=<directory>\n"
"    The location to place the pid and umid files.\n\n"
);

static void remove_umid_dir(void)
{
    char dir[strlen(uml_dir) + UMID_LEN + 1], err;

    sprintf(dir, "%s%s", uml_dir, umid);
    err = remove_files_and_dir(dir);
    if (err)
        printf("remove_umid_dir - remove_files_and_dir failed with "
               "err = %d\n", err);
}

__uml_exitcall(remove_umid_dir);