libs/vr/libpdx_uds/ipc_helper.cpp - platform/frameworks/native - Gitiles

 #include "uds/ipc_helper.h"

 #include <alloca.h>
 #include <errno.h>
 #include <log/log.h>
 #include <poll.h>
 #include <string.h>
 #include <sys/inotify.h>
 #include <sys/param.h>
 #include <sys/socket.h>

 #include <algorithm>

 #include <pdx/service.h>
 #include <pdx/utility.h>

 namespace android {
 namespace pdx {
 namespace uds {

 uint32_t kMagicPreamble = 0x7564736d;  // 'udsm'.

 struct MessagePreamble {
   uint32_t magic{0};
   uint32_t data_size{0};
   uint32_t fd_count{0};
 };

 Status<void> SendPayload::Send(int socket_fd) {
   return Send(socket_fd, nullptr);
 }

 Status<void> SendPayload::Send(int socket_fd, const ucred* cred) {
   MessagePreamble preamble;
   preamble.magic = kMagicPreamble;
   preamble.data_size = buffer_.size();
   preamble.fd_count = file_handles_.size();

   ssize_t ret =
       RETRY_EINTR(send(socket_fd, &preamble, sizeof(preamble), MSG_NOSIGNAL));
   if (ret < 0)
     return ErrorStatus(errno);
   if (ret != sizeof(preamble))
     return ErrorStatus(EIO);

   msghdr msg = {};
   iovec recv_vect = {buffer_.data(), buffer_.size()};
   msg.msg_iov = &recv_vect;
   msg.msg_iovlen = 1;

   if (cred || !file_handles_.empty()) {
     const size_t fd_bytes = file_handles_.size() * sizeof(int);
     msg.msg_controllen = (cred ? CMSG_SPACE(sizeof(ucred)) : 0) +
                          (fd_bytes == 0 ? 0 : CMSG_SPACE(fd_bytes));
     msg.msg_control = alloca(msg.msg_controllen);

     cmsghdr* control = CMSG_FIRSTHDR(&msg);
     if (cred) {
       control->cmsg_level = SOL_SOCKET;
       control->cmsg_type = SCM_CREDENTIALS;
       control->cmsg_len = CMSG_LEN(sizeof(ucred));
       memcpy(CMSG_DATA(control), cred, sizeof(ucred));
       control = CMSG_NXTHDR(&msg, control);
     }

     if (fd_bytes) {
       control->cmsg_level = SOL_SOCKET;
       control->cmsg_type = SCM_RIGHTS;
       control->cmsg_len = CMSG_LEN(fd_bytes);
       memcpy(CMSG_DATA(control), file_handles_.data(), fd_bytes);
     }
   }

   ret = RETRY_EINTR(sendmsg(socket_fd, &msg, MSG_NOSIGNAL));
   if (ret < 0)
     return ErrorStatus(errno);
   if (static_cast<size_t>(ret) != buffer_.size())
     return ErrorStatus(EIO);
   return {};
 }

 // MessageWriter
 void* SendPayload::GetNextWriteBufferSection(size_t size) {
   return buffer_.grow_by(size);
 }

 OutputResourceMapper* SendPayload::GetOutputResourceMapper() { return this; }

 // OutputResourceMapper
 FileReference SendPayload::PushFileHandle(const LocalHandle& handle) {
   if (handle) {
     const int ref = file_handles_.size();
     file_handles_.push_back(handle.Get());
     return ref;
   } else {
     return handle.Get();
   }
 }

 FileReference SendPayload::PushFileHandle(const BorrowedHandle& handle) {
   if (handle) {
     const int ref = file_handles_.size();
     file_handles_.push_back(handle.Get());
     return ref;
   } else {
     return handle.Get();
   }
 }

 FileReference SendPayload::PushFileHandle(const RemoteHandle& handle) {
   return handle.Get();
 }

 ChannelReference SendPayload::PushChannelHandle(
     const LocalChannelHandle& /*handle*/) {
   return -1;
 }
 ChannelReference SendPayload::PushChannelHandle(
     const BorrowedChannelHandle& /*handle*/) {
   return -1;
 }
 ChannelReference SendPayload::PushChannelHandle(
     const RemoteChannelHandle& /*handle*/) {
   return -1;
 }

 Status<void> ReceivePayload::Receive(int socket_fd) {
   return Receive(socket_fd, nullptr);
 }

 Status<void> ReceivePayload::Receive(int socket_fd, ucred* cred) {
   MessagePreamble preamble;
   ssize_t ret =
       RETRY_EINTR(recv(socket_fd, &preamble, sizeof(preamble), MSG_WAITALL));
   if (ret < 0)
     return ErrorStatus(errno);
   if (ret != sizeof(preamble) || preamble.magic != kMagicPreamble)
     return ErrorStatus(EIO);

   buffer_.resize(preamble.data_size);
   file_handles_.clear();
   read_pos_ = 0;

   msghdr msg = {};
   iovec recv_vect = {buffer_.data(), buffer_.size()};
   msg.msg_iov = &recv_vect;
   msg.msg_iovlen = 1;

   if (cred || preamble.fd_count) {
     const size_t receive_fd_bytes = preamble.fd_count * sizeof(int);
     msg.msg_controllen =
         (cred ? CMSG_SPACE(sizeof(ucred)) : 0) +
         (receive_fd_bytes == 0 ? 0 : CMSG_SPACE(receive_fd_bytes));
     msg.msg_control = alloca(msg.msg_controllen);
   }

   ret = RETRY_EINTR(recvmsg(socket_fd, &msg, MSG_WAITALL));
   if (ret < 0)
     return ErrorStatus(errno);
   if (static_cast<uint32_t>(ret) != preamble.data_size)
     return ErrorStatus(EIO);

   bool cred_available = false;
   file_handles_.reserve(preamble.fd_count);
   cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
   while (cmsg) {
     if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_CREDENTIALS &&
         cred && cmsg->cmsg_len == CMSG_LEN(sizeof(ucred))) {
       cred_available = true;
       memcpy(cred, CMSG_DATA(cmsg), sizeof(ucred));
     } else if (cmsg->cmsg_level == SOL_SOCKET &&
                cmsg->cmsg_type == SCM_RIGHTS) {
       socklen_t payload_len = cmsg->cmsg_len - CMSG_LEN(0);
       const int* fds = reinterpret_cast<const int*>(CMSG_DATA(cmsg));
       size_t fd_count = payload_len / sizeof(int);
       std::transform(fds, fds + fd_count, std::back_inserter(file_handles_),
                      [](int fd) { return LocalHandle{fd}; });
     }
     cmsg = CMSG_NXTHDR(&msg, cmsg);
   }

   if (cred && !cred_available) {
     return ErrorStatus(EIO);
   }

   return {};
 }

 // MessageReader
 MessageReader::BufferSection ReceivePayload::GetNextReadBufferSection() {
   return {buffer_.data() + read_pos_, &*buffer_.end()};
 }

 void ReceivePayload::ConsumeReadBufferSectionData(const void* new_start) {
   read_pos_ = PointerDistance(new_start, buffer_.data());
 }

 InputResourceMapper* ReceivePayload::GetInputResourceMapper() { return this; }

 // InputResourceMapper
 bool ReceivePayload::GetFileHandle(FileReference ref, LocalHandle* handle) {
   if (ref < 0) {
     *handle = LocalHandle{ref};
     return true;
   }
   if (static_cast<size_t>(ref) > file_handles_.size())
     return false;
   *handle = std::move(file_handles_[ref]);
   return true;
 }

 bool ReceivePayload::GetChannelHandle(ChannelReference /*ref*/,
                                       LocalChannelHandle* /*handle*/) {
   return false;
 }

 Status<void> SendData(int socket_fd, const void* data, size_t size) {
   ssize_t size_written = RETRY_EINTR(send(socket_fd, data, size, MSG_NOSIGNAL));
   if (size_written < 0)
     return ErrorStatus(errno);
   if (static_cast<size_t>(size_written) != size)
     return ErrorStatus(EIO);
   return {};
 }

 Status<void> SendDataVector(int socket_fd, const iovec* data, size_t count) {
   msghdr msg = {};
   msg.msg_iov = const_cast<iovec*>(data);
   msg.msg_iovlen = count;
   ssize_t size_written = RETRY_EINTR(sendmsg(socket_fd, &msg, MSG_NOSIGNAL));
   if (size_written < 0)
     return ErrorStatus(errno);
   if (static_cast<size_t>(size_written) != CountVectorSize(data, count))
     return ErrorStatus(EIO);
   return {};
 }

 Status<void> ReceiveData(int socket_fd, void* data, size_t size) {
   ssize_t size_read = RETRY_EINTR(recv(socket_fd, data, size, MSG_WAITALL));
   if (size_read < 0)
     return ErrorStatus(errno);
   if (static_cast<size_t>(size_read) != size)
     return ErrorStatus(EIO);
   return {};
 }

 Status<void> ReceiveDataVector(int socket_fd, const iovec* data, size_t count) {
   msghdr msg = {};
   msg.msg_iov = const_cast<iovec*>(data);
   msg.msg_iovlen = count;
   ssize_t size_read = RETRY_EINTR(recvmsg(socket_fd, &msg, MSG_WAITALL));
   if (size_read < 0)
     return ErrorStatus(errno);
   if (static_cast<size_t>(size_read) != CountVectorSize(data, count))
     return ErrorStatus(EIO);
   return {};
 }

 size_t CountVectorSize(const iovec* vector, size_t count) {
   return std::accumulate(
       vector, vector + count, size_t{0},
       [](size_t size, const iovec& vec) { return size + vec.iov_len; });
 }

 void InitRequest(android::pdx::uds::RequestHeader<BorrowedHandle>* request,
                  int opcode, uint32_t send_len, uint32_t max_recv_len,
                  bool is_impulse) {
   request->op = opcode;
   request->cred.pid = getpid();
   request->cred.uid = geteuid();
   request->cred.gid = getegid();
   request->send_len = send_len;
   request->max_recv_len = max_recv_len;
   request->is_impulse = is_impulse;
 }

 Status<void> WaitForEndpoint(const std::string& endpoint_path,
                              int64_t timeout_ms) {
   // Endpoint path must be absolute.
   if (endpoint_path.empty() || endpoint_path.front() != '/')
     return ErrorStatus(EINVAL);

   // Create inotify fd.
   LocalHandle fd{inotify_init()};
   if (!fd)
     return ErrorStatus(errno);

   // Set the inotify fd to non-blocking.
   int ret = fcntl(fd.Get(), F_GETFL);
   fcntl(fd.Get(), F_SETFL, ret | O_NONBLOCK);

   // Setup the pollfd.
   pollfd pfd = {fd.Get(), POLLIN, 0};

   // Find locations of each path separator.
   std::vector<size_t> separators{0};  // The path is absolute, so '/' is at #0.
   size_t pos = endpoint_path.find('/', 1);
   while (pos != std::string::npos) {
     separators.push_back(pos);
     pos = endpoint_path.find('/', pos + 1);
   }
   separators.push_back(endpoint_path.size());

   // Walk down the path, checking for existence and waiting if needed.
   pos = 1;
   size_t links = 0;
   std::string current;
   while (pos < separators.size() && links <= MAXSYMLINKS) {
     std::string previous = current;
     current = endpoint_path.substr(0, separators[pos]);

     // Check for existence; proceed to setup a watch if not.
     if (access(current.c_str(), F_OK) < 0) {
       if (errno != ENOENT)
         return ErrorStatus(errno);

       // Extract the name of the path component to wait for.
       std::string next = current.substr(
           separators[pos - 1] + 1, separators[pos] - separators[pos - 1] - 1);

       // Add a watch on the last existing directory we reach.
       int wd = inotify_add_watch(
           fd.Get(), previous.c_str(),
           IN_CREATE | IN_DELETE_SELF | IN_MOVE_SELF | IN_MOVED_TO);
       if (wd < 0) {
         if (errno != ENOENT)
           return ErrorStatus(errno);
         // Restart at the beginning if previous was deleted.
         links = 0;
         current.clear();
         pos = 1;
         continue;
       }

       // Make sure current didn't get created before the watch was added.
       ret = access(current.c_str(), F_OK);
       if (ret < 0) {
         if (errno != ENOENT)
           return ErrorStatus(errno);

         bool exit_poll = false;
         while (!exit_poll) {
           // Wait for an event or timeout.
           ret = poll(&pfd, 1, timeout_ms);
           if (ret <= 0)
             return ErrorStatus(ret == 0 ? ETIMEDOUT : errno);

           // Read events.
           char buffer[sizeof(inotify_event) + NAME_MAX + 1];

           ret = read(fd.Get(), buffer, sizeof(buffer));
           if (ret < 0) {
             if (errno == EAGAIN || errno == EWOULDBLOCK)
               continue;
             else
               return ErrorStatus(errno);
           } else if (static_cast<size_t>(ret) < sizeof(struct inotify_event)) {
             return ErrorStatus(EIO);
           }

           auto* event = reinterpret_cast<const inotify_event*>(buffer);
           auto* end = reinterpret_cast<const inotify_event*>(buffer + ret);
           while (event < end) {
             std::string event_for;
             if (event->len > 0)
               event_for = event->name;

             if (event->mask & (IN_CREATE | IN_MOVED_TO)) {
               // See if this is the droid we're looking for.
               if (next == event_for) {
                 exit_poll = true;
                 break;
               }
             } else if (event->mask & (IN_DELETE_SELF | IN_MOVE_SELF)) {
               // Restart at the beginning if our watch dir is deleted.
               links = 0;
               current.clear();
               pos = 0;
               exit_poll = true;
               break;
             }

             event = reinterpret_cast<const inotify_event*>(AdvancePointer(
                 event, sizeof(struct inotify_event) + event->len));
           }  // while (event < end)
         }    // while (!exit_poll)
       }      // Current dir doesn't exist.
       ret = inotify_rm_watch(fd.Get(), wd);
       if (ret < 0 && errno != EINVAL)
         return ErrorStatus(errno);
     }  // if (access(current.c_str(), F_OK) < 0)

     // Check for symbolic link and update link count.
     struct stat stat_buf;
     ret = lstat(current.c_str(), &stat_buf);
     if (ret < 0 && errno != ENOENT)
       return ErrorStatus(errno);
     else if (ret == 0 && S_ISLNK(stat_buf.st_mode))
       links++;
     pos++;
   }  // while (pos < separators.size() && links <= MAXSYMLINKS)

   return {};
 }

 }  // namespace uds
 }  // namespace pdx
 }  // namespace android
	#include "uds/ipc_helper.h"

	#include <alloca.h>
	#include <errno.h>
	#include <log/log.h>
	#include <poll.h>
	#include <string.h>
	#include <sys/inotify.h>
	#include <sys/param.h>
	#include <sys/socket.h>

	#include <algorithm>

	#include <pdx/service.h>
	#include <pdx/utility.h>

	namespace android {
	namespace pdx {
	namespace uds {

	uint32_t kMagicPreamble = 0x7564736d; // 'udsm'.

	struct MessagePreamble {
	uint32_t magic{0};
	uint32_t data_size{0};
	uint32_t fd_count{0};
	};

	Status<void> SendPayload::Send(int socket_fd) {
	return Send(socket_fd, nullptr);
	}

	Status<void> SendPayload::Send(int socket_fd, const ucred* cred) {
	MessagePreamble preamble;
	preamble.magic = kMagicPreamble;
	preamble.data_size = buffer_.size();
	preamble.fd_count = file_handles_.size();

	ssize_t ret =
	RETRY_EINTR(send(socket_fd, &preamble, sizeof(preamble), MSG_NOSIGNAL));
	if (ret < 0)
	return ErrorStatus(errno);
	if (ret != sizeof(preamble))
	return ErrorStatus(EIO);

	msghdr msg = {};
	iovec recv_vect = {buffer_.data(), buffer_.size()};
	msg.msg_iov = &recv_vect;
	msg.msg_iovlen = 1;

	if (cred \|\| !file_handles_.empty()) {
	const size_t fd_bytes = file_handles_.size() * sizeof(int);
	msg.msg_controllen = (cred ? CMSG_SPACE(sizeof(ucred)) : 0) +
	(fd_bytes == 0 ? 0 : CMSG_SPACE(fd_bytes));
	msg.msg_control = alloca(msg.msg_controllen);

	cmsghdr* control = CMSG_FIRSTHDR(&msg);
	if (cred) {
	control->cmsg_level = SOL_SOCKET;
	control->cmsg_type = SCM_CREDENTIALS;
	control->cmsg_len = CMSG_LEN(sizeof(ucred));
	memcpy(CMSG_DATA(control), cred, sizeof(ucred));
	control = CMSG_NXTHDR(&msg, control);
	}

	if (fd_bytes) {
	control->cmsg_level = SOL_SOCKET;
	control->cmsg_type = SCM_RIGHTS;
	control->cmsg_len = CMSG_LEN(fd_bytes);
	memcpy(CMSG_DATA(control), file_handles_.data(), fd_bytes);
	}
	}

	ret = RETRY_EINTR(sendmsg(socket_fd, &msg, MSG_NOSIGNAL));
	if (ret < 0)
	return ErrorStatus(errno);
	if (static_cast<size_t>(ret) != buffer_.size())
	return ErrorStatus(EIO);
	return {};
	}

	// MessageWriter
	void* SendPayload::GetNextWriteBufferSection(size_t size) {
	return buffer_.grow_by(size);
	}

	OutputResourceMapper* SendPayload::GetOutputResourceMapper() { return this; }

	// OutputResourceMapper
	FileReference SendPayload::PushFileHandle(const LocalHandle& handle) {
	if (handle) {
	const int ref = file_handles_.size();
	file_handles_.push_back(handle.Get());
	return ref;
	} else {
	return handle.Get();
	}
	}

	FileReference SendPayload::PushFileHandle(const BorrowedHandle& handle) {
	if (handle) {
	const int ref = file_handles_.size();
	file_handles_.push_back(handle.Get());
	return ref;
	} else {
	return handle.Get();
	}
	}

	FileReference SendPayload::PushFileHandle(const RemoteHandle& handle) {
	return handle.Get();
	}

	ChannelReference SendPayload::PushChannelHandle(
	const LocalChannelHandle& /handle/) {
	return -1;
	}
	ChannelReference SendPayload::PushChannelHandle(
	const BorrowedChannelHandle& /handle/) {
	return -1;
	}
	ChannelReference SendPayload::PushChannelHandle(
	const RemoteChannelHandle& /handle/) {
	return -1;
	}

	Status<void> ReceivePayload::Receive(int socket_fd) {
	return Receive(socket_fd, nullptr);
	}

	Status<void> ReceivePayload::Receive(int socket_fd, ucred* cred) {
	MessagePreamble preamble;
	ssize_t ret =
	RETRY_EINTR(recv(socket_fd, &preamble, sizeof(preamble), MSG_WAITALL));
	if (ret < 0)
	return ErrorStatus(errno);
	if (ret != sizeof(preamble) \|\| preamble.magic != kMagicPreamble)
	return ErrorStatus(EIO);

	buffer_.resize(preamble.data_size);
	file_handles_.clear();
	read_pos_ = 0;

	msghdr msg = {};
	iovec recv_vect = {buffer_.data(), buffer_.size()};
	msg.msg_iov = &recv_vect;
	msg.msg_iovlen = 1;

	if (cred \|\| preamble.fd_count) {
	const size_t receive_fd_bytes = preamble.fd_count * sizeof(int);
	msg.msg_controllen =
	(cred ? CMSG_SPACE(sizeof(ucred)) : 0) +
	(receive_fd_bytes == 0 ? 0 : CMSG_SPACE(receive_fd_bytes));
	msg.msg_control = alloca(msg.msg_controllen);
	}

	ret = RETRY_EINTR(recvmsg(socket_fd, &msg, MSG_WAITALL));
	if (ret < 0)
	return ErrorStatus(errno);
	if (static_cast<uint32_t>(ret) != preamble.data_size)
	return ErrorStatus(EIO);

	bool cred_available = false;
	file_handles_.reserve(preamble.fd_count);
	cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
	while (cmsg) {
	if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_CREDENTIALS &&
	cred && cmsg->cmsg_len == CMSG_LEN(sizeof(ucred))) {
	cred_available = true;
	memcpy(cred, CMSG_DATA(cmsg), sizeof(ucred));
	} else if (cmsg->cmsg_level == SOL_SOCKET &&
	cmsg->cmsg_type == SCM_RIGHTS) {
	socklen_t payload_len = cmsg->cmsg_len - CMSG_LEN(0);
	const int* fds = reinterpret_cast<const int*>(CMSG_DATA(cmsg));
	size_t fd_count = payload_len / sizeof(int);
	std::transform(fds, fds + fd_count, std::back_inserter(file_handles_),
	[](int fd) { return LocalHandle{fd}; });
	}
	cmsg = CMSG_NXTHDR(&msg, cmsg);
	}

	if (cred && !cred_available) {
	return ErrorStatus(EIO);
	}

	return {};
	}

	// MessageReader
	MessageReader::BufferSection ReceivePayload::GetNextReadBufferSection() {
	return {buffer_.data() + read_pos_, &*buffer_.end()};
	}

	void ReceivePayload::ConsumeReadBufferSectionData(const void* new_start) {
	read_pos_ = PointerDistance(new_start, buffer_.data());
	}

	InputResourceMapper* ReceivePayload::GetInputResourceMapper() { return this; }

	// InputResourceMapper
	bool ReceivePayload::GetFileHandle(FileReference ref, LocalHandle* handle) {
	if (ref < 0) {
	*handle = LocalHandle{ref};
	return true;
	}
	if (static_cast<size_t>(ref) > file_handles_.size())
	return false;
	*handle = std::move(file_handles_[ref]);
	return true;
	}

	bool ReceivePayload::GetChannelHandle(ChannelReference /ref/,
	LocalChannelHandle* /handle/) {
	return false;
	}

	Status<void> SendData(int socket_fd, const void* data, size_t size) {
	ssize_t size_written = RETRY_EINTR(send(socket_fd, data, size, MSG_NOSIGNAL));
	if (size_written < 0)
	return ErrorStatus(errno);
	if (static_cast<size_t>(size_written) != size)
	return ErrorStatus(EIO);
	return {};
	}

	Status<void> SendDataVector(int socket_fd, const iovec* data, size_t count) {
	msghdr msg = {};
	msg.msg_iov = const_cast<iovec*>(data);
	msg.msg_iovlen = count;
	ssize_t size_written = RETRY_EINTR(sendmsg(socket_fd, &msg, MSG_NOSIGNAL));
	if (size_written < 0)
	return ErrorStatus(errno);
	if (static_cast<size_t>(size_written) != CountVectorSize(data, count))
	return ErrorStatus(EIO);
	return {};
	}

	Status<void> ReceiveData(int socket_fd, void* data, size_t size) {
	ssize_t size_read = RETRY_EINTR(recv(socket_fd, data, size, MSG_WAITALL));
	if (size_read < 0)
	return ErrorStatus(errno);
	if (static_cast<size_t>(size_read) != size)
	return ErrorStatus(EIO);
	return {};
	}

	Status<void> ReceiveDataVector(int socket_fd, const iovec* data, size_t count) {
	msghdr msg = {};
	msg.msg_iov = const_cast<iovec*>(data);
	msg.msg_iovlen = count;
	ssize_t size_read = RETRY_EINTR(recvmsg(socket_fd, &msg, MSG_WAITALL));
	if (size_read < 0)
	return ErrorStatus(errno);
	if (static_cast<size_t>(size_read) != CountVectorSize(data, count))
	return ErrorStatus(EIO);
	return {};
	}

	size_t CountVectorSize(const iovec* vector, size_t count) {
	return std::accumulate(
	vector, vector + count, size_t{0},
	[](size_t size, const iovec& vec) { return size + vec.iov_len; });
	}

	void InitRequest(android::pdx::uds::RequestHeader<BorrowedHandle>* request,
	int opcode, uint32_t send_len, uint32_t max_recv_len,
	bool is_impulse) {
	request->op = opcode;
	request->cred.pid = getpid();
	request->cred.uid = geteuid();
	request->cred.gid = getegid();
	request->send_len = send_len;
	request->max_recv_len = max_recv_len;
	request->is_impulse = is_impulse;
	}

	Status<void> WaitForEndpoint(const std::string& endpoint_path,
	int64_t timeout_ms) {
	// Endpoint path must be absolute.
	if (endpoint_path.empty() \|\| endpoint_path.front() != '/')
	return ErrorStatus(EINVAL);

	// Create inotify fd.
	LocalHandle fd{inotify_init()};
	if (!fd)
	return ErrorStatus(errno);

	// Set the inotify fd to non-blocking.
	int ret = fcntl(fd.Get(), F_GETFL);
	fcntl(fd.Get(), F_SETFL, ret \| O_NONBLOCK);

	// Setup the pollfd.
	pollfd pfd = {fd.Get(), POLLIN, 0};

	// Find locations of each path separator.
	std::vector<size_t> separators{0}; // The path is absolute, so '/' is at #0.
	size_t pos = endpoint_path.find('/', 1);
	while (pos != std::string::npos) {
	separators.push_back(pos);
	pos = endpoint_path.find('/', pos + 1);
	}
	separators.push_back(endpoint_path.size());

	// Walk down the path, checking for existence and waiting if needed.
	pos = 1;
	size_t links = 0;
	std::string current;
	while (pos < separators.size() && links <= MAXSYMLINKS) {
	std::string previous = current;
	current = endpoint_path.substr(0, separators[pos]);

	// Check for existence; proceed to setup a watch if not.
	if (access(current.c_str(), F_OK) < 0) {
	if (errno != ENOENT)
	return ErrorStatus(errno);

	// Extract the name of the path component to wait for.
	std::string next = current.substr(
	separators[pos - 1] + 1, separators[pos] - separators[pos - 1] - 1);

	// Add a watch on the last existing directory we reach.
	int wd = inotify_add_watch(
	fd.Get(), previous.c_str(),
	IN_CREATE \| IN_DELETE_SELF \| IN_MOVE_SELF \| IN_MOVED_TO);
	if (wd < 0) {
	if (errno != ENOENT)
	return ErrorStatus(errno);
	// Restart at the beginning if previous was deleted.
	links = 0;
	current.clear();
	pos = 1;
	continue;
	}

	// Make sure current didn't get created before the watch was added.
	ret = access(current.c_str(), F_OK);
	if (ret < 0) {
	if (errno != ENOENT)
	return ErrorStatus(errno);

	bool exit_poll = false;
	while (!exit_poll) {
	// Wait for an event or timeout.
	ret = poll(&pfd, 1, timeout_ms);
	if (ret <= 0)
	return ErrorStatus(ret == 0 ? ETIMEDOUT : errno);

	// Read events.
	char buffer[sizeof(inotify_event) + NAME_MAX + 1];

	ret = read(fd.Get(), buffer, sizeof(buffer));
	if (ret < 0) {
	if (errno == EAGAIN \|\| errno == EWOULDBLOCK)
	continue;
	else
	return ErrorStatus(errno);
	} else if (static_cast<size_t>(ret) < sizeof(struct inotify_event)) {
	return ErrorStatus(EIO);
	}

	auto* event = reinterpret_cast<const inotify_event*>(buffer);
	auto* end = reinterpret_cast<const inotify_event*>(buffer + ret);
	while (event < end) {
	std::string event_for;
	if (event->len > 0)
	event_for = event->name;

	if (event->mask & (IN_CREATE \| IN_MOVED_TO)) {
	// See if this is the droid we're looking for.
	if (next == event_for) {
	exit_poll = true;
	break;
	}
	} else if (event->mask & (IN_DELETE_SELF \| IN_MOVE_SELF)) {
	// Restart at the beginning if our watch dir is deleted.
	links = 0;
	current.clear();
	pos = 0;
	exit_poll = true;
	break;
	}

	event = reinterpret_cast<const inotify_event*>(AdvancePointer(
	event, sizeof(struct inotify_event) + event->len));
	} // while (event < end)
	} // while (!exit_poll)
	} // Current dir doesn't exist.
	ret = inotify_rm_watch(fd.Get(), wd);
	if (ret < 0 && errno != EINVAL)
	return ErrorStatus(errno);
	} // if (access(current.c_str(), F_OK) < 0)

	// Check for symbolic link and update link count.
	struct stat stat_buf;
	ret = lstat(current.c_str(), &stat_buf);
	if (ret < 0 && errno != ENOENT)
	return ErrorStatus(errno);
	else if (ret == 0 && S_ISLNK(stat_buf.st_mode))
	links++;
	pos++;
	} // while (pos < separators.size() && links <= MAXSYMLINKS)

	return {};
	}

	} // namespace uds
	} // namespace pdx
	} // namespace android