libc/bionic/system_properties.c - platform/bionic - Git at Google

 /*
  * Copyright (C) 2008 The Android Open Source Project
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *  * Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  *  * Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <stddef.h>
 #include <errno.h>
 #include <poll.h>
 #include <fcntl.h>
 #include <stdbool.h>

 #include <sys/mman.h>

 #include <sys/socket.h>
 #include <sys/un.h>
 #include <sys/select.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <netinet/in.h>
 #include <unistd.h>

 #define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
 #include <sys/_system_properties.h>

 #include <sys/atomics.h>

 struct prop_area {
     unsigned volatile count;
     unsigned volatile serial;
     unsigned magic;
     unsigned version;
     unsigned toc[1];
 };

 typedef struct prop_area prop_area;

 struct prop_info {
     char name[PROP_NAME_MAX];
     unsigned volatile serial;
     char value[PROP_VALUE_MAX];
 };

 typedef struct prop_info prop_info;

 static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
 static char property_filename[PATH_MAX] = PROP_FILENAME;

 prop_area *__system_property_regions__[PA_REGION_COUNT] = { NULL, };

 static int get_fd_from_env(void)
 {
     char *env = getenv("ANDROID_PROPERTY_WORKSPACE");

     if (!env) {
         return -1;
     }

     return atoi(env);
 }

 static int map_prop_region_rw(size_t region)
 {
     prop_area *pa;
     int fd;
     size_t offset = region * PA_SIZE;

     if (__system_property_regions__[region]) {
         return 0;
     }

     /* dev is a tmpfs that we can use to carve a shared workspace
      * out of, so let's do that...
      */
     fd = open(property_filename, O_RDWR | O_CREAT | O_NOFOLLOW, 0644);
     if (fd < 0) {
         if (errno == EACCES) {
             /* for consistency with the case where the process has already
              * mapped the page in and segfaults when trying to write to it
              */
             abort();
         }
         return -1;
     }

     if (ftruncate(fd, offset + PA_SIZE) < 0)
         goto out;

     pa = mmap(NULL, PA_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
     if(pa == MAP_FAILED)
         goto out;

     memset(pa, 0, PA_SIZE);
     pa->magic = PROP_AREA_MAGIC;
     pa->version = PROP_AREA_VERSION;

     /* plug into the lib property services */
     __system_property_regions__[region] = pa;

     close(fd);
     return 0;

 out:
     close(fd);
     return -1;
 }

 int __system_property_set_filename(const char *filename)
 {
     size_t len = strlen(filename);
     if (len >= sizeof(property_filename))
         return -1;

     strcpy(property_filename, filename);
     return 0;
 }

 int __system_property_area_init()
 {
     return map_prop_region_rw(0);
 }

 static int map_prop_region(size_t region)
 {
     bool fromFile = true;
     bool swapped;
     size_t offset = region * PA_SIZE;
     int result = -1;

     if(__system_property_regions__[region]) {
         return 0;
     }

     int fd = open(property_filename, O_RDONLY | O_NOFOLLOW);

     if ((fd < 0) && (errno == ENOENT)) {
         /*
          * For backwards compatibility, if the file doesn't
          * exist, we use the environment to get the file descriptor.
          * For security reasons, we only use this backup if the kernel
          * returns ENOENT. We don't want to use the backup if the kernel
          * returns other errors such as ENOMEM or ENFILE, since it
          * might be possible for an external program to trigger this
          * condition.
          */
         fd = get_fd_from_env();
         fromFile = false;
     }

     if (fd < 0) {
         return -1;
     }

     struct stat fd_stat;
     if (fstat(fd, &fd_stat) < 0) {
         goto cleanup;
     }

     if ((fd_stat.st_uid != 0)
             || (fd_stat.st_gid != 0)
             || ((fd_stat.st_mode & (S_IWGRP | S_IWOTH)) != 0)
             || (fd_stat.st_size < offset + PA_SIZE) ) {
         goto cleanup;
     }

     prop_area *pa = mmap(NULL, PA_SIZE, PROT_READ, MAP_SHARED, fd, offset);

     if (pa == MAP_FAILED) {
         goto cleanup;
     }

     if((pa->magic != PROP_AREA_MAGIC) || (pa->version != PROP_AREA_VERSION)) {
         munmap(pa, PA_SIZE);
         goto cleanup;
     }

     result = 0;
     swapped = __sync_bool_compare_and_swap(&__system_property_regions__[region],
             NULL, pa);
     if (!swapped) {
         /**
          * In the event of a race either mapping is equally good, so
          * the thread that lost can just throw its mapping away and proceed as
          * normal.
          */
         munmap(pa, PA_SIZE);
     }

 cleanup:
     if (fromFile) {
         close(fd);
     }

     return result;
 }

 int __system_properties_init()
 {
     return map_prop_region(0);
 }

 int __system_property_foreach(
         void (*propfn)(const prop_info *pi, void *cookie),
         void *cookie)
 {
     size_t region;

     for (region = 0; region < PA_REGION_COUNT; region++) {
         prop_area *pa;
         unsigned i;

         int err = map_prop_region(region);
         if (err < 0)
             break;
         pa = __system_property_regions__[region];

         for (i = 0; i < pa->count; i++) {
             unsigned entry = pa->toc[i];
             prop_info *pi = TOC_TO_INFO(pa, entry);
             propfn(pi, cookie);
         }
     }

     return 0;
 }

 const prop_info *__system_property_find_nth(unsigned n)
 {
     size_t region = n / PA_COUNT_MAX;
     prop_area *pa;

     int err = map_prop_region(region);
     if (err < 0)
         return NULL;
     pa = __system_property_regions__[region];

     if((n % PA_COUNT_MAX) >= pa->count) {
         return 0;
     } else {
         return TOC_TO_INFO(pa, pa->toc[n]);
     }
 }

 const prop_info *__system_property_find(const char *name)
 {
     unsigned len = strlen(name);
     size_t region;

     if (len >= PROP_NAME_MAX)
         return 0;
     if (len < 1)
         return 0;

     for (region = 0; region < PA_REGION_COUNT; region++) {
         prop_area *pa;
         unsigned count;
         unsigned *toc;
         prop_info *pi;

         int err = map_prop_region(region);
         if (err < 0)
             return 0;
         pa = __system_property_regions__[region];
         count = pa->count;
         toc = pa->toc;

         while(count--) {
             unsigned entry = *toc++;
             if(TOC_NAME_LEN(entry) != len) continue;

             pi = TOC_TO_INFO(pa, entry);
             if(memcmp(name, pi->name, len)) continue;

             return pi;
         }
     }

     return 0;
 }

 int __system_property_read(const prop_info *pi, char *name, char *value)
 {
     unsigned serial, len;

     for(;;) {
         serial = pi->serial;
         while(SERIAL_DIRTY(serial)) {
             __futex_wait((volatile void *)&pi->serial, serial, 0);
             serial = pi->serial;
         }
         len = SERIAL_VALUE_LEN(serial);
         memcpy(value, pi->value, len + 1);
         if(serial == pi->serial) {
             if(name != 0) {
                 strcpy(name, pi->name);
             }
             return len;
         }
     }
 }

 int __system_property_get(const char *name, char *value)
 {
     const prop_info *pi = __system_property_find(name);

     if(pi != 0) {
         return __system_property_read(pi, 0, value);
     } else {
         value[0] = 0;
         return 0;
     }
 }


 static int send_prop_msg(prop_msg *msg)
 {
     struct pollfd pollfds[1];
     struct sockaddr_un addr;
     socklen_t alen;
     size_t namelen;
     int s;
     int r;
     int result = -1;

     s = socket(AF_LOCAL, SOCK_STREAM, 0);
     if(s < 0) {
         return result;
     }

     memset(&addr, 0, sizeof(addr));
     namelen = strlen(property_service_socket);
     strlcpy(addr.sun_path, property_service_socket, sizeof addr.sun_path);
     addr.sun_family = AF_LOCAL;
     alen = namelen + offsetof(struct sockaddr_un, sun_path) + 1;

     if(TEMP_FAILURE_RETRY(connect(s, (struct sockaddr *) &addr, alen)) < 0) {
         close(s);
         return result;
     }

     r = TEMP_FAILURE_RETRY(send(s, msg, sizeof(prop_msg), 0));

     if(r == sizeof(prop_msg)) {
         // We successfully wrote to the property server but now we
         // wait for the property server to finish its work.  It
         // acknowledges its completion by closing the socket so we
         // poll here (on nothing), waiting for the socket to close.
         // If you 'adb shell setprop foo bar' you'll see the POLLHUP
         // once the socket closes.  Out of paranoia we cap our poll
         // at 250 ms.
         pollfds[0].fd = s;
         pollfds[0].events = 0;
         r = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
         if (r == 1 && (pollfds[0].revents & POLLHUP) != 0) {
             result = 0;
         } else {
             // Ignore the timeout and treat it like a success anyway.
             // The init process is single-threaded and its property
             // service is sometimes slow to respond (perhaps it's off
             // starting a child process or something) and thus this
             // times out and the caller thinks it failed, even though
             // it's still getting around to it.  So we fake it here,
             // mostly for ctl.* properties, but we do try and wait 250
             // ms so callers who do read-after-write can reliably see
             // what they've written.  Most of the time.
             // TODO: fix the system properties design.
             result = 0;
         }
     }

     close(s);
     return result;
 }

 int __system_property_set(const char *key, const char *value)
 {
     int err;
     prop_msg msg;

     if(key == 0) return -1;
     if(value == 0) value = "";
     if(strlen(key) >= PROP_NAME_MAX) return -1;
     if(strlen(value) >= PROP_VALUE_MAX) return -1;

     memset(&msg, 0, sizeof msg);
     msg.cmd = PROP_MSG_SETPROP;
     strlcpy(msg.name, key, sizeof msg.name);
     strlcpy(msg.value, value, sizeof msg.value);

     err = send_prop_msg(&msg);
     if(err < 0) {
         return err;
     }

     return 0;
 }

 int __system_property_wait(const prop_info *pi)
 {
     unsigned n;
     if(pi == 0) {
         prop_area *pa = __system_property_regions__[0];
         n = pa->serial;
         do {
             __futex_wait(&pa->serial, n, 0);
         } while(n == pa->serial);
     } else {
         n = pi->serial;
         do {
             __futex_wait((volatile void *)&pi->serial, n, 0);
         } while(n == pi->serial);
     }
     return 0;
 }

 int __system_property_update(prop_info *pi, const char *value, unsigned int len)
 {
     prop_area *pa = __system_property_regions__[0];

     if (len >= PROP_VALUE_MAX)
         return -1;

     pi->serial = pi->serial | 1;
     memcpy(pi->value, value, len + 1);
     pi->serial = (len << 24) | ((pi->serial + 1) & 0xffffff);
     __futex_wake(&pi->serial, INT32_MAX);

     pa->serial++;
     __futex_wake(&pa->serial, INT32_MAX);

     return 0;
 }

 int __system_property_add(const char *name, unsigned int namelen,
             const char *value, unsigned int valuelen)
 {
     prop_area *pa;
     prop_info *pa_info_array;
     prop_info *pi;
     size_t region;

     if (namelen >= PROP_NAME_MAX)
         return -1;
     if (valuelen >= PROP_VALUE_MAX)
         return -1;
     if (namelen < 1)
         return -1;

     for (region = 0; region < PA_REGION_COUNT; region++)
     {
         int err = map_prop_region_rw(region);
         if (err < 0)
             return -1;

         pa = __system_property_regions__[region];

         if (pa->count < PA_COUNT_MAX)
             break;
     }

     if (region == PA_REGION_COUNT)
         return -1;

     pa_info_array = (void*) (((char*) pa) + PA_INFO_START);
     pi = pa_info_array + pa->count;
     pi->serial = (valuelen << 24);
     memcpy(pi->name, name, namelen + 1);
     memcpy(pi->value, value, valuelen + 1);

     pa->toc[pa->count] = (namelen << 24) | (((unsigned) pi) - ((unsigned) pa));

     pa->count++;
     pa->serial++;
     __futex_wake(&pa->serial, INT32_MAX);

     return 0;
 }

 unsigned int __system_property_serial(const prop_info *pi)
 {
     return pi->serial;
 }

 unsigned int __system_property_wait_any(unsigned int serial)
 {
     prop_area *pa = __system_property_regions__[0];

     do {
         __futex_wait(&pa->serial, serial, 0);
     } while(pa->serial == serial);

     return pa->serial;
 }
	/*
	* Copyright (C) 2008 The Android Open Source Project
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* * Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* * Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in
	* the documentation and/or other materials provided with the
	* distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
	* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
	* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
	* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
	* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
	* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
	* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
	* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	* SUCH DAMAGE.
	*/
	#include <stdio.h>
	#include <stdint.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <stddef.h>
	#include <errno.h>
	#include <poll.h>
	#include <fcntl.h>
	#include <stdbool.h>

	#include <sys/mman.h>

	#include <sys/socket.h>
	#include <sys/un.h>
	#include <sys/select.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <netinet/in.h>
	#include <unistd.h>

	#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
	#include <sys/_system_properties.h>

	#include <sys/atomics.h>

	struct prop_area {
	unsigned volatile count;
	unsigned volatile serial;
	unsigned magic;
	unsigned version;
	unsigned toc[1];
	};

	typedef struct prop_area prop_area;

	struct prop_info {
	char name[PROP_NAME_MAX];
	unsigned volatile serial;
	char value[PROP_VALUE_MAX];
	};

	typedef struct prop_info prop_info;

	static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
	static char property_filename[PATH_MAX] = PROP_FILENAME;

	prop_area *__system_property_regions__[PA_REGION_COUNT] = { NULL, };

	static int get_fd_from_env(void)
	{
	char *env = getenv("ANDROID_PROPERTY_WORKSPACE");

	if (!env) {
	return -1;
	}

	return atoi(env);
	}

	static int map_prop_region_rw(size_t region)
	{
	prop_area *pa;
	int fd;
	size_t offset = region * PA_SIZE;

	if (__system_property_regions__[region]) {
	return 0;
	}

	/* dev is a tmpfs that we can use to carve a shared workspace
	* out of, so let's do that...
	*/
	fd = open(property_filename, O_RDWR \| O_CREAT \| O_NOFOLLOW, 0644);
	if (fd < 0) {
	if (errno == EACCES) {
	/* for consistency with the case where the process has already
	* mapped the page in and segfaults when trying to write to it
	*/
	abort();
	}
	return -1;
	}

	if (ftruncate(fd, offset + PA_SIZE) < 0)
	goto out;

	pa = mmap(NULL, PA_SIZE, PROT_READ \| PROT_WRITE, MAP_SHARED, fd, offset);
	if(pa == MAP_FAILED)
	goto out;

	memset(pa, 0, PA_SIZE);
	pa->magic = PROP_AREA_MAGIC;
	pa->version = PROP_AREA_VERSION;

	/* plug into the lib property services */
	__system_property_regions__[region] = pa;

	close(fd);
	return 0;

	out:
	close(fd);
	return -1;
	}

	int __system_property_set_filename(const char *filename)
	{
	size_t len = strlen(filename);
	if (len >= sizeof(property_filename))
	return -1;

	strcpy(property_filename, filename);
	return 0;
	}

	int __system_property_area_init()
	{
	return map_prop_region_rw(0);
	}

	static int map_prop_region(size_t region)
	{
	bool fromFile = true;
	bool swapped;
	size_t offset = region * PA_SIZE;
	int result = -1;

	if(__system_property_regions__[region]) {
	return 0;
	}

	int fd = open(property_filename, O_RDONLY \| O_NOFOLLOW);

	if ((fd < 0) && (errno == ENOENT)) {
	/*
	* For backwards compatibility, if the file doesn't
	* exist, we use the environment to get the file descriptor.
	* For security reasons, we only use this backup if the kernel
	* returns ENOENT. We don't want to use the backup if the kernel
	* returns other errors such as ENOMEM or ENFILE, since it
	* might be possible for an external program to trigger this
	* condition.
	*/
	fd = get_fd_from_env();
	fromFile = false;
	}

	if (fd < 0) {
	return -1;
	}

	struct stat fd_stat;
	if (fstat(fd, &fd_stat) < 0) {
	goto cleanup;
	}

	if ((fd_stat.st_uid != 0)
	\|\| (fd_stat.st_gid != 0)
	\|\| ((fd_stat.st_mode & (S_IWGRP \| S_IWOTH)) != 0)
	\|\| (fd_stat.st_size < offset + PA_SIZE) ) {
	goto cleanup;
	}

	prop_area *pa = mmap(NULL, PA_SIZE, PROT_READ, MAP_SHARED, fd, offset);

	if (pa == MAP_FAILED) {
	goto cleanup;
	}

	if((pa->magic != PROP_AREA_MAGIC) \|\| (pa->version != PROP_AREA_VERSION)) {
	munmap(pa, PA_SIZE);
	goto cleanup;
	}

	result = 0;
	swapped = __sync_bool_compare_and_swap(&__system_property_regions__[region],
	NULL, pa);
	if (!swapped) {
	/**
	* In the event of a race either mapping is equally good, so
	* the thread that lost can just throw its mapping away and proceed as
	* normal.
	*/
	munmap(pa, PA_SIZE);
	}

	cleanup:
	if (fromFile) {
	close(fd);
	}

	return result;
	}

	int __system_properties_init()
	{
	return map_prop_region(0);
	}

	int __system_property_foreach(
	void (propfn)(const prop_info pi, void *cookie),
	void *cookie)
	{
	size_t region;

	for (region = 0; region < PA_REGION_COUNT; region++) {
	prop_area *pa;
	unsigned i;

	int err = map_prop_region(region);
	if (err < 0)
	break;
	pa = __system_property_regions__[region];

	for (i = 0; i < pa->count; i++) {
	unsigned entry = pa->toc[i];
	prop_info *pi = TOC_TO_INFO(pa, entry);
	propfn(pi, cookie);
	}
	}

	return 0;
	}

	const prop_info *__system_property_find_nth(unsigned n)
	{
	size_t region = n / PA_COUNT_MAX;
	prop_area *pa;

	int err = map_prop_region(region);
	if (err < 0)
	return NULL;
	pa = __system_property_regions__[region];

	if((n % PA_COUNT_MAX) >= pa->count) {
	return 0;
	} else {
	return TOC_TO_INFO(pa, pa->toc[n]);
	}
	}

	const prop_info __system_property_find(const char name)
	{
	unsigned len = strlen(name);
	size_t region;

	if (len >= PROP_NAME_MAX)
	return 0;
	if (len < 1)
	return 0;

	for (region = 0; region < PA_REGION_COUNT; region++) {
	prop_area *pa;
	unsigned count;
	unsigned *toc;
	prop_info *pi;

	int err = map_prop_region(region);
	if (err < 0)
	return 0;
	pa = __system_property_regions__[region];
	count = pa->count;
	toc = pa->toc;

	while(count--) {
	unsigned entry = *toc++;
	if(TOC_NAME_LEN(entry) != len) continue;

	pi = TOC_TO_INFO(pa, entry);
	if(memcmp(name, pi->name, len)) continue;

	return pi;
	}
	}

	return 0;
	}

	int __system_property_read(const prop_info pi, char name, char *value)
	{
	unsigned serial, len;

	for(;;) {
	serial = pi->serial;
	while(SERIAL_DIRTY(serial)) {
	__futex_wait((volatile void *)&pi->serial, serial, 0);
	serial = pi->serial;
	}
	len = SERIAL_VALUE_LEN(serial);
	memcpy(value, pi->value, len + 1);
	if(serial == pi->serial) {
	if(name != 0) {
	strcpy(name, pi->name);
	}
	return len;
	}
	}
	}

	int __system_property_get(const char name, char value)
	{
	const prop_info *pi = __system_property_find(name);

	if(pi != 0) {
	return __system_property_read(pi, 0, value);
	} else {
	value[0] = 0;
	return 0;
	}
	}


	static int send_prop_msg(prop_msg *msg)
	{
	struct pollfd pollfds[1];
	struct sockaddr_un addr;
	socklen_t alen;
	size_t namelen;
	int s;
	int r;
	int result = -1;

	s = socket(AF_LOCAL, SOCK_STREAM, 0);
	if(s < 0) {
	return result;
	}

	memset(&addr, 0, sizeof(addr));
	namelen = strlen(property_service_socket);
	strlcpy(addr.sun_path, property_service_socket, sizeof addr.sun_path);
	addr.sun_family = AF_LOCAL;
	alen = namelen + offsetof(struct sockaddr_un, sun_path) + 1;

	if(TEMP_FAILURE_RETRY(connect(s, (struct sockaddr *) &addr, alen)) < 0) {
	close(s);
	return result;
	}

	r = TEMP_FAILURE_RETRY(send(s, msg, sizeof(prop_msg), 0));

	if(r == sizeof(prop_msg)) {
	// We successfully wrote to the property server but now we
	// wait for the property server to finish its work. It
	// acknowledges its completion by closing the socket so we
	// poll here (on nothing), waiting for the socket to close.
	// If you 'adb shell setprop foo bar' you'll see the POLLHUP
	// once the socket closes. Out of paranoia we cap our poll
	// at 250 ms.
	pollfds[0].fd = s;
	pollfds[0].events = 0;
	r = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
	if (r == 1 && (pollfds[0].revents & POLLHUP) != 0) {
	result = 0;
	} else {
	// Ignore the timeout and treat it like a success anyway.
	// The init process is single-threaded and its property
	// service is sometimes slow to respond (perhaps it's off
	// starting a child process or something) and thus this
	// times out and the caller thinks it failed, even though
	// it's still getting around to it. So we fake it here,
	// mostly for ctl.* properties, but we do try and wait 250
	// ms so callers who do read-after-write can reliably see
	// what they've written. Most of the time.
	// TODO: fix the system properties design.
	result = 0;
	}
	}

	close(s);
	return result;
	}

	int __system_property_set(const char key, const char value)
	{
	int err;
	prop_msg msg;

	if(key == 0) return -1;
	if(value == 0) value = "";
	if(strlen(key) >= PROP_NAME_MAX) return -1;
	if(strlen(value) >= PROP_VALUE_MAX) return -1;

	memset(&msg, 0, sizeof msg);
	msg.cmd = PROP_MSG_SETPROP;
	strlcpy(msg.name, key, sizeof msg.name);
	strlcpy(msg.value, value, sizeof msg.value);

	err = send_prop_msg(&msg);
	if(err < 0) {
	return err;
	}

	return 0;
	}

	int __system_property_wait(const prop_info *pi)
	{
	unsigned n;
	if(pi == 0) {
	prop_area *pa = __system_property_regions__[0];
	n = pa->serial;
	do {
	__futex_wait(&pa->serial, n, 0);
	} while(n == pa->serial);
	} else {
	n = pi->serial;
	do {
	__futex_wait((volatile void *)&pi->serial, n, 0);
	} while(n == pi->serial);
	}
	return 0;
	}

	int __system_property_update(prop_info pi, const char value, unsigned int len)
	{
	prop_area *pa = __system_property_regions__[0];

	if (len >= PROP_VALUE_MAX)
	return -1;

	pi->serial = pi->serial \| 1;
	memcpy(pi->value, value, len + 1);
	pi->serial = (len << 24) \| ((pi->serial + 1) & 0xffffff);
	__futex_wake(&pi->serial, INT32_MAX);

	pa->serial++;
	__futex_wake(&pa->serial, INT32_MAX);

	return 0;
	}

	int __system_property_add(const char *name, unsigned int namelen,
	const char *value, unsigned int valuelen)
	{
	prop_area *pa;
	prop_info *pa_info_array;
	prop_info *pi;
	size_t region;

	if (namelen >= PROP_NAME_MAX)
	return -1;
	if (valuelen >= PROP_VALUE_MAX)
	return -1;
	if (namelen < 1)
	return -1;

	for (region = 0; region < PA_REGION_COUNT; region++)
	{
	int err = map_prop_region_rw(region);
	if (err < 0)
	return -1;

	pa = __system_property_regions__[region];

	if (pa->count < PA_COUNT_MAX)
	break;
	}

	if (region == PA_REGION_COUNT)
	return -1;

	pa_info_array = (void) (((char) pa) + PA_INFO_START);
	pi = pa_info_array + pa->count;
	pi->serial = (valuelen << 24);
	memcpy(pi->name, name, namelen + 1);
	memcpy(pi->value, value, valuelen + 1);

	pa->toc[pa->count] = (namelen << 24) \| (((unsigned) pi) - ((unsigned) pa));

	pa->count++;
	pa->serial++;
	__futex_wake(&pa->serial, INT32_MAX);

	return 0;
	}

	unsigned int __system_property_serial(const prop_info *pi)
	{
	return pi->serial;
	}

	unsigned int __system_property_wait_any(unsigned int serial)
	{
	prop_area *pa = __system_property_regions__[0];

	do {
	__futex_wait(&pa->serial, serial, 0);
	} while(pa->serial == serial);

	return pa->serial;
	}