rootdev.c - platform/external/rootdev - Gitiles

 /* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * Implements root device discovery via sysfs with optional bells and whistles.
  */

 #include "rootdev.h"

 #include <ctype.h>
 #include <dirent.h>
 #include <err.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>

 /*
  * Limit prevents endless looping to find slave.
  * We currently have at most 2 levels, this allows
  * for future growth.
  */
 #define MAX_SLAVE_DEPTH 8

 static const char *kDefaultSearchPath = "/sys/block";
 static const char *kDefaultDevPath = "/dev/block";

 /* Encode the root device structuring here for Chromium OS */
 static const char kActiveRoot[] = "/dev/ACTIVE_ROOT";
 static const char kRootDev[] = "/dev/ROOT";
 static const char kRootA[] = "/dev/ROOT0";
 static const char kRootB[] = "/dev/ROOT1";

 struct part_config {
   const char *name;
   int offset;
 };

 #define CHROMEOS_PRIMARY_PARTITION 3
 static const struct part_config kPrimaryPart[] = { { kRootA,    0 },
                                                    { kRootDev, -3 },
                                                    { kRootB,    2 } };
 #define CHROMEOS_SECONDARY_PARTITION 5
 static const struct part_config kSecondaryPart[] = { { kRootB,    0 },
                                                      { kRootDev, -5 },
                                                      { kRootA,   -2 } };

 /* The number of entries in a part_config so we could add RootC easily. */
 static const int kPartitionEntries = 3;

 /* Converts a file of %u:%u -> dev_t. */
 static dev_t devt_from_file(const char *file) {
   char candidate[10];  /* TODO(wad) system-provided constant? */
   ssize_t bytes = 0;
   unsigned int major_num = 0;
   unsigned int minor_num = 0;
   dev_t dev = 0;
   int fd = -1;

   /* Never hang. Either get the data or return 0. */
   fd = open(file, O_NONBLOCK | O_RDONLY);
   if (fd < 0)
     return 0;
   bytes = read(fd, candidate, sizeof(candidate));
   close(fd);

   /* 0:0 should be considered the minimum size. */
   if (bytes < 3)
     return 0;
   candidate[bytes] = 0;
   if (sscanf(candidate, "%u:%u", &major_num, &minor_num) == 2) {
     /* candidate's size artificially limits the size of the converted
      * %u to safely convert to a signed int. */
     dev = makedev(major_num, minor_num);
   }
   return dev;
 }

 /* Walks sysfs and recurses into any directory/link that represents
  * a block device to find sub-devices (partitions) for dev.
  * If dev == 0, the name fo the first device in the directory will be returned.
  * Returns the device's name in "name" */
 static int match_sysfs_device(char *name, size_t name_len,
                               const char *basedir, dev_t *dev, int depth) {
   int found = -1;
   size_t basedir_len;
   DIR *dirp = NULL;
   struct dirent *entry = NULL;
   struct dirent *next = NULL;
   char *working_path = NULL;
   long working_path_size = 0;

   if (!name || !name_len || !basedir || !dev) {
     warnx("match_sysfs_device: invalid arguments supplied");
     return -1;
   }
   basedir_len = strlen(basedir);
   if (!basedir_len) {
     warnx("match_sysfs_device: basedir must not be empty");
     return -1;
   }

   errno = 0;
   dirp = opendir(basedir);
   if (!dirp) {
      /* Don't complain if the directory doesn't exist. */
      if (errno != ENOENT)
        warn("match_sysfs_device:opendir(%s)", basedir);
      return found;
   }

   /* Grab a platform appropriate path to work with.
    * Ideally, this won't vary under sys/block. */
   working_path_size = pathconf(basedir, _PC_NAME_MAX) + 1;
   /* Fallback to PATH_MAX on any pathconf error. */
   if (working_path_size < 0)
     working_path_size = PATH_MAX;

   working_path = malloc(working_path_size);
   if (!working_path) {
     warn("malloc(dirent)");
     closedir(dirp);
     return found;
   }

   /* Allocate a properly sized entry. */
   entry = malloc(offsetof(struct dirent, d_name) + working_path_size);
   if (!entry) {
     warn("malloc(dirent)");
     free(working_path);
     closedir(dirp);
     return found;
   }

   while (readdir_r(dirp, entry, &next) == 0 && next) {
     size_t candidate_len = strlen(entry->d_name);
     size_t path_len = 0;
     dev_t found_devt = 0;
     /* Ignore the usual */
     if (!strcmp(entry->d_name, ".") || !strcmp(entry->d_name, ".."))
       continue;
     /* TODO(wad) determine how to best bubble up this case. */
     if (candidate_len > name_len)
       continue;
     /* Only traverse directories or symlinks (to directories ideally) */
     switch (entry->d_type) {
     case DT_UNKNOWN:
     case DT_DIR:
     case DT_LNK:
       break;
     default:
       continue;
     }
     /* Determine path to block device number */
     path_len = snprintf(working_path, working_path_size, "%s/%s/dev",
                         basedir, entry->d_name);
     /* Ignore if truncation occurs. */
     if (path_len != candidate_len + basedir_len + 5)
       continue;

     found_devt = devt_from_file(working_path);
     /* *dev == 0 is a wildcard. */
     if (!*dev || found_devt == *dev) {
       snprintf(name, name_len, "%s", entry->d_name);
       *dev = found_devt;
       found = 1;
       break;
     }

     /* Prevent infinite recursion on symlink loops by limiting depth. */
     if (depth > 5)
       break;

     /* Recurse one level for devices that may have a matching partition. */
     if (major(found_devt) == major(*dev) && minor(*dev) > minor(found_devt)) {
       sprintf(working_path, "%s/%s", basedir, entry->d_name);
       found = match_sysfs_device(name, name_len, working_path, dev, depth + 1);
       if (found > 0)
         break;
     }
   }

   free(working_path);
   free(entry);
   closedir(dirp);
   return found;
 }

 const char *rootdev_get_partition(const char *dst, size_t len) {
   const char *end = dst + strnlen(dst, len);
   const char *part = end - 1;
   if (!len)
     return NULL;

   if (!isdigit(*part--))
     return NULL;

   while (part > dst && isdigit(*part)) part--;
   part++;

   if (part >= end)
     return NULL;

   return part;
 }

 void rootdev_strip_partition(char *dst, size_t len) {
   char *part = (char *)rootdev_get_partition(dst, len);
   if (!part)
     return;
   /* For devices that end with a digit, the kernel uses a 'p'
    * as a separator. E.g., mmcblk1p2. */
   if (*(part - 1) == 'p')
     part--;
   *part = '\0';
 }

 int rootdev_symlink_active(const char *path) {
   int ret = 0;
   /* Don't overwrite an existing link. */
   errno = 0;
   if ((symlink(path, kActiveRoot)) && errno != EEXIST) {
     warn("failed to symlink %s -> %s", kActiveRoot, path);
     ret = -1;
   }
   return ret;
 }

 int rootdev_get_device(char *dst, size_t size, dev_t dev,
                        const char *search) {
   struct stat active_root_statbuf;

   if (search == NULL)
     search = kDefaultSearchPath;

   /* Check if the -s symlink exists. */
   if ((stat(kActiveRoot, &active_root_statbuf) == 0) &&
       active_root_statbuf.st_rdev == dev) {
     /* Note, if the link is not fully qualified, this won't be
      * either. */
     ssize_t len = readlink(kActiveRoot, dst, PATH_MAX);
     if (len > 0) {
       dst[len] = 0;
       return 0;
     }
     /* If readlink fails or is empty, fall through */
   }

   snprintf(dst, size, "%s", search);
   if (match_sysfs_device(dst, size, dst, &dev, 0) <= 0) {
     fprintf (stderr, "unable to find match\n");
     return 1;
   }

   return 0;
 }

 /*
  * rootdev_get_device_slave returns results in slave which
  * may be the original device or the name of the slave.
  *
  * Because slave and device may point to the same data,
  * must be careful how they are handled because slave
  * is modified (can't use snprintf).
  */
 void rootdev_get_device_slave(char *slave, size_t size, dev_t *dev,
                               const char *device, const char *search) {
   char dst[PATH_MAX];
   int len = 0;
   int i;

   if (search == NULL)
     search = kDefaultSearchPath;

   /*
    * With stacked device mappers, we have to chain through all the levels
    * and find the last device. For example, verity can be stacked on bootcache
    * that is stacked on a disk partition.
    */
   if (slave != device)
     strncpy(slave, device, size);
   slave[size - 1] = '\0';
   for (i = 0; i < MAX_SLAVE_DEPTH; i++) {
     len = snprintf(dst, sizeof(dst), "%s/%s/slaves", search, slave);
     if (len != strlen(device) + strlen(search) + 8) {
       warnx("rootdev_get_device_slave: device name too long");
       return;
     }
     *dev = 0;
     if (match_sysfs_device(slave, size, dst, dev, 0) <= 0) {
       return;
     }
   }
   warnx("slave depth greater than %d at %s", i, slave);
 }

 int rootdev_create_devices(const char *name, dev_t dev, bool symlink) {
   int ret = 0;
   unsigned int major_num = major(dev);
   unsigned int minor_num = minor(dev);
   int i;
   const struct part_config *config;
   const char *part_s = rootdev_get_partition(name, strlen(name));

   if (part_s == NULL) {
     warnx("create_devices: unable to determine partition");
     return -1;
   }

   switch (atoi(part_s)) {
   case CHROMEOS_PRIMARY_PARTITION:
     config = kPrimaryPart;
     break;
   case CHROMEOS_SECONDARY_PARTITION:
     config = kSecondaryPart;
     break;
   default:
     warnx("create_devices: unable to determine partition: %s",
           part_s);
     return -1;
   }

   for (i = 0; i < kPartitionEntries; ++i) {
     dev = makedev(major_num, minor_num + config[i].offset);
     errno = 0;
     if (mknod(config[i].name,
               S_IFBLK | S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH,
               dev) && errno != EEXIST) {
       warn("failed to create %s", config[i].name);
       return -1;
     }
   }

   if (symlink)
     ret = rootdev_symlink_active(config[0].name);
   return ret;
 }

 int rootdev_get_path(char *path, size_t size, const char *device,
                      const char *dev_path) {
   int path_len;

   if (!dev_path)
     dev_path = kDefaultDevPath;

   if (!path || !size || !device)
     return -1;

   path_len = snprintf(path, size, "%s/%s", dev_path, device);
   if (path_len != strlen(dev_path) + 1 + strlen(device))
     return -1;

   // TODO(bsimonnet): We should check that |path| exists and is the right
   // device. We don't do this currently as OEMs can add custom SELinux rules
   // which may prevent us from accessing this.
   // See b/24267261.

   return 0;
 }

 int rootdev_wrapper(char *path, size_t size,
                     bool full, bool strip,
                     dev_t *dev,
                     const char *search, const char *dev_path) {
   int res = 0;
   char devname[PATH_MAX];
   if (!search)
     search = kDefaultSearchPath;
   if (!dev_path)
    dev_path = kDefaultDevPath;
   if (!dev)
     return -1;

   res = rootdev_get_device(devname, sizeof(devname), *dev, search);
   if (res != 0)
     return res;

   if (full)
     rootdev_get_device_slave(devname, sizeof(devname), dev, devname,
                              search);

   /* TODO(wad) we should really just track the block dev, partition number, and
    *           dev path.  When we rewrite this, we can track all the sysfs info
    *           in the class. */
   if (strip) {
     /* When we strip the partition, we don't want get_path to return non-zero
      * because of dev mismatch.  Passing in 0 tells it to not test. */
     *dev = 0;
     rootdev_strip_partition(devname, size);
   }

   res = rootdev_get_path(path, size, devname, dev_path);

   return res;
 }

 int rootdev(char *path, size_t size, bool full, bool strip) {
   struct stat root_statbuf;
   dev_t _root_dev, *root_dev = &_root_dev;

   /* Yields the containing dev_t in st_dev. */
   if (stat("/data", &root_statbuf) != 0)
     return -1;

   /* Some ABIs (like mips o32) are broken and the st_dev field isn't actually
    * a dev_t.  In that case, pass a pointer to a local dev_t who we took care
    * of truncating the value into.  On sane arches, gcc can optimize this to
    * the same code, so should only be a penalty when the ABI is broken. */
   if (sizeof(root_statbuf.st_dev) == sizeof(*root_dev)) {
     /* Cast is OK since we verified size here. */
     root_dev = (dev_t *)&root_statbuf.st_dev;
   } else {
     *root_dev = root_statbuf.st_dev;
   }

   return rootdev_wrapper(path,
                          size,
                          full,
                          strip,
                          root_dev,
                          NULL,  /* default /sys dir */
                          NULL);  /* default /dev dir */
 }
	/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*
	* Implements root device discovery via sysfs with optional bells and whistles.
	*/

	#include "rootdev.h"

	#include <ctype.h>
	#include <dirent.h>
	#include <err.h>
	#include <errno.h>
	#include <fcntl.h>
	#include <stdbool.h>
	#include <stddef.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <unistd.h>

	/*
	* Limit prevents endless looping to find slave.
	* We currently have at most 2 levels, this allows
	* for future growth.
	*/
	#define MAX_SLAVE_DEPTH 8

	static const char *kDefaultSearchPath = "/sys/block";
	static const char *kDefaultDevPath = "/dev/block";

	/* Encode the root device structuring here for Chromium OS */
	static const char kActiveRoot[] = "/dev/ACTIVE_ROOT";
	static const char kRootDev[] = "/dev/ROOT";
	static const char kRootA[] = "/dev/ROOT0";
	static const char kRootB[] = "/dev/ROOT1";

	struct part_config {
	const char *name;
	int offset;
	};

	#define CHROMEOS_PRIMARY_PARTITION 3
	static const struct part_config kPrimaryPart[] = { { kRootA, 0 },
	{ kRootDev, -3 },
	{ kRootB, 2 } };
	#define CHROMEOS_SECONDARY_PARTITION 5
	static const struct part_config kSecondaryPart[] = { { kRootB, 0 },
	{ kRootDev, -5 },
	{ kRootA, -2 } };

	/* The number of entries in a part_config so we could add RootC easily. */
	static const int kPartitionEntries = 3;

	/* Converts a file of %u:%u -> dev_t. */
	static dev_t devt_from_file(const char *file) {
	char candidate[10]; /* TODO(wad) system-provided constant? */
	ssize_t bytes = 0;
	unsigned int major_num = 0;
	unsigned int minor_num = 0;
	dev_t dev = 0;
	int fd = -1;

	/* Never hang. Either get the data or return 0. */
	fd = open(file, O_NONBLOCK \| O_RDONLY);
	if (fd < 0)
	return 0;
	bytes = read(fd, candidate, sizeof(candidate));
	close(fd);

	/* 0:0 should be considered the minimum size. */
	if (bytes < 3)
	return 0;
	candidate[bytes] = 0;
	if (sscanf(candidate, "%u:%u", &major_num, &minor_num) == 2) {
	/* candidate's size artificially limits the size of the converted
	* %u to safely convert to a signed int. */
	dev = makedev(major_num, minor_num);
	}
	return dev;
	}

	/* Walks sysfs and recurses into any directory/link that represents
	* a block device to find sub-devices (partitions) for dev.
	* If dev == 0, the name fo the first device in the directory will be returned.
	* Returns the device's name in "name" */
	static int match_sysfs_device(char *name, size_t name_len,
	const char basedir, dev_t dev, int depth) {
	int found = -1;
	size_t basedir_len;
	DIR *dirp = NULL;
	struct dirent *entry = NULL;
	struct dirent *next = NULL;
	char *working_path = NULL;
	long working_path_size = 0;

	if (!name \|\| !name_len \|\| !basedir \|\| !dev) {
	warnx("match_sysfs_device: invalid arguments supplied");
	return -1;
	}
	basedir_len = strlen(basedir);
	if (!basedir_len) {
	warnx("match_sysfs_device: basedir must not be empty");
	return -1;
	}

	errno = 0;
	dirp = opendir(basedir);
	if (!dirp) {
	/* Don't complain if the directory doesn't exist. */
	if (errno != ENOENT)
	warn("match_sysfs_device:opendir(%s)", basedir);
	return found;
	}

	/* Grab a platform appropriate path to work with.
	* Ideally, this won't vary under sys/block. */
	working_path_size = pathconf(basedir, _PC_NAME_MAX) + 1;
	/* Fallback to PATH_MAX on any pathconf error. */
	if (working_path_size < 0)
	working_path_size = PATH_MAX;

	working_path = malloc(working_path_size);
	if (!working_path) {
	warn("malloc(dirent)");
	closedir(dirp);
	return found;
	}

	/* Allocate a properly sized entry. */
	entry = malloc(offsetof(struct dirent, d_name) + working_path_size);
	if (!entry) {
	warn("malloc(dirent)");
	free(working_path);
	closedir(dirp);
	return found;
	}

	while (readdir_r(dirp, entry, &next) == 0 && next) {
	size_t candidate_len = strlen(entry->d_name);
	size_t path_len = 0;
	dev_t found_devt = 0;
	/* Ignore the usual */
	if (!strcmp(entry->d_name, ".") \|\| !strcmp(entry->d_name, ".."))
	continue;
	/* TODO(wad) determine how to best bubble up this case. */
	if (candidate_len > name_len)
	continue;
	/* Only traverse directories or symlinks (to directories ideally) */
	switch (entry->d_type) {
	case DT_UNKNOWN:
	case DT_DIR:
	case DT_LNK:
	break;
	default:
	continue;
	}
	/* Determine path to block device number */
	path_len = snprintf(working_path, working_path_size, "%s/%s/dev",
	basedir, entry->d_name);
	/* Ignore if truncation occurs. */
	if (path_len != candidate_len + basedir_len + 5)
	continue;

	found_devt = devt_from_file(working_path);
	/* dev == 0 is a wildcard. /
	if (!dev \|\| found_devt == dev) {
	snprintf(name, name_len, "%s", entry->d_name);
	*dev = found_devt;
	found = 1;
	break;
	}

	/* Prevent infinite recursion on symlink loops by limiting depth. */
	if (depth > 5)
	break;

	/* Recurse one level for devices that may have a matching partition. */
	if (major(found_devt) == major(dev) && minor(dev) > minor(found_devt)) {
	sprintf(working_path, "%s/%s", basedir, entry->d_name);
	found = match_sysfs_device(name, name_len, working_path, dev, depth + 1);
	if (found > 0)
	break;
	}
	}

	free(working_path);
	free(entry);
	closedir(dirp);
	return found;
	}

	const char rootdev_get_partition(const char dst, size_t len) {
	const char *end = dst + strnlen(dst, len);
	const char *part = end - 1;
	if (!len)
	return NULL;

	if (!isdigit(*part--))
	return NULL;

	while (part > dst && isdigit(*part)) part--;
	part++;

	if (part >= end)
	return NULL;

	return part;
	}

	void rootdev_strip_partition(char *dst, size_t len) {
	char part = (char )rootdev_get_partition(dst, len);
	if (!part)
	return;
	/* For devices that end with a digit, the kernel uses a 'p'
	* as a separator. E.g., mmcblk1p2. */
	if (*(part - 1) == 'p')
	part--;
	*part = '\0';
	}

	int rootdev_symlink_active(const char *path) {
	int ret = 0;
	/* Don't overwrite an existing link. */
	errno = 0;
	if ((symlink(path, kActiveRoot)) && errno != EEXIST) {
	warn("failed to symlink %s -> %s", kActiveRoot, path);
	ret = -1;
	}
	return ret;
	}

	int rootdev_get_device(char *dst, size_t size, dev_t dev,
	const char *search) {
	struct stat active_root_statbuf;

	if (search == NULL)
	search = kDefaultSearchPath;

	/* Check if the -s symlink exists. */
	if ((stat(kActiveRoot, &active_root_statbuf) == 0) &&
	active_root_statbuf.st_rdev == dev) {
	/* Note, if the link is not fully qualified, this won't be
	* either. */
	ssize_t len = readlink(kActiveRoot, dst, PATH_MAX);
	if (len > 0) {
	dst[len] = 0;
	return 0;
	}
	/* If readlink fails or is empty, fall through */
	}

	snprintf(dst, size, "%s", search);
	if (match_sysfs_device(dst, size, dst, &dev, 0) <= 0) {
	fprintf (stderr, "unable to find match\n");
	return 1;
	}

	return 0;
	}

	/*
	* rootdev_get_device_slave returns results in slave which
	* may be the original device or the name of the slave.
	*
	* Because slave and device may point to the same data,
	* must be careful how they are handled because slave
	* is modified (can't use snprintf).
	*/
	void rootdev_get_device_slave(char slave, size_t size, dev_t dev,
	const char device, const char search) {
	char dst[PATH_MAX];
	int len = 0;
	int i;

	if (search == NULL)
	search = kDefaultSearchPath;

	/*
	* With stacked device mappers, we have to chain through all the levels
	* and find the last device. For example, verity can be stacked on bootcache
	* that is stacked on a disk partition.
	*/
	if (slave != device)
	strncpy(slave, device, size);
	slave[size - 1] = '\0';
	for (i = 0; i < MAX_SLAVE_DEPTH; i++) {
	len = snprintf(dst, sizeof(dst), "%s/%s/slaves", search, slave);
	if (len != strlen(device) + strlen(search) + 8) {
	warnx("rootdev_get_device_slave: device name too long");
	return;
	}
	*dev = 0;
	if (match_sysfs_device(slave, size, dst, dev, 0) <= 0) {
	return;
	}
	}
	warnx("slave depth greater than %d at %s", i, slave);
	}

	int rootdev_create_devices(const char *name, dev_t dev, bool symlink) {
	int ret = 0;
	unsigned int major_num = major(dev);
	unsigned int minor_num = minor(dev);
	int i;
	const struct part_config *config;
	const char *part_s = rootdev_get_partition(name, strlen(name));

	if (part_s == NULL) {
	warnx("create_devices: unable to determine partition");
	return -1;
	}

	switch (atoi(part_s)) {
	case CHROMEOS_PRIMARY_PARTITION:
	config = kPrimaryPart;
	break;
	case CHROMEOS_SECONDARY_PARTITION:
	config = kSecondaryPart;
	break;
	default:
	warnx("create_devices: unable to determine partition: %s",
	part_s);
	return -1;
	}

	for (i = 0; i < kPartitionEntries; ++i) {
	dev = makedev(major_num, minor_num + config[i].offset);
	errno = 0;
	if (mknod(config[i].name,
	S_IFBLK \| S_IRUSR \| S_IWUSR \| S_IRGRP \| S_IROTH,
	dev) && errno != EEXIST) {
	warn("failed to create %s", config[i].name);
	return -1;
	}
	}

	if (symlink)
	ret = rootdev_symlink_active(config[0].name);
	return ret;
	}

	int rootdev_get_path(char path, size_t size, const char device,
	const char *dev_path) {
	int path_len;

	if (!dev_path)
	dev_path = kDefaultDevPath;

	if (!path \|\| !size \|\| !device)
	return -1;

	path_len = snprintf(path, size, "%s/%s", dev_path, device);
	if (path_len != strlen(dev_path) + 1 + strlen(device))
	return -1;

	// TODO(bsimonnet): We should check that \|path\| exists and is the right
	// device. We don't do this currently as OEMs can add custom SELinux rules
	// which may prevent us from accessing this.
	// See b/24267261.

	return 0;
	}

	int rootdev_wrapper(char *path, size_t size,
	bool full, bool strip,
	dev_t *dev,
	const char search, const char dev_path) {
	int res = 0;
	char devname[PATH_MAX];
	if (!search)
	search = kDefaultSearchPath;
	if (!dev_path)
	dev_path = kDefaultDevPath;
	if (!dev)
	return -1;

	res = rootdev_get_device(devname, sizeof(devname), *dev, search);
	if (res != 0)
	return res;

	if (full)
	rootdev_get_device_slave(devname, sizeof(devname), dev, devname,
	search);

	/* TODO(wad) we should really just track the block dev, partition number, and
	* dev path. When we rewrite this, we can track all the sysfs info
	* in the class. */
	if (strip) {
	/* When we strip the partition, we don't want get_path to return non-zero
	* because of dev mismatch. Passing in 0 tells it to not test. */
	*dev = 0;
	rootdev_strip_partition(devname, size);
	}

	res = rootdev_get_path(path, size, devname, dev_path);

	return res;
	}

	int rootdev(char *path, size_t size, bool full, bool strip) {
	struct stat root_statbuf;
	dev_t _root_dev, *root_dev = &_root_dev;

	/* Yields the containing dev_t in st_dev. */
	if (stat("/data", &root_statbuf) != 0)
	return -1;

	/* Some ABIs (like mips o32) are broken and the st_dev field isn't actually
	* a dev_t. In that case, pass a pointer to a local dev_t who we took care
	* of truncating the value into. On sane arches, gcc can optimize this to
	* the same code, so should only be a penalty when the ABI is broken. */
	if (sizeof(root_statbuf.st_dev) == sizeof(*root_dev)) {
	/* Cast is OK since we verified size here. */
	root_dev = (dev_t *)&root_statbuf.st_dev;
	} else {
	*root_dev = root_statbuf.st_dev;
	}

	return rootdev_wrapper(path,
	size,
	full,
	strip,
	root_dev,
	NULL, /* default /sys dir */
	NULL); /* default /dev dir */
	}