tequilaOS/platform_system_core
2
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

ueventd: duplicate /dev/ashmem

Browse source 
We want ashmem to only be used via libcutils API, with long-term goal
being deprecation of ashmem with memfd. To do that we route libcutils to
a new source of ashmem fds. We then phase out uses of /dev/ashmem that
doesn't go through libcutils using SELinux.

In Q, we introduced ashmemd as the source of ashmem fds to libcutils.
However, having a separate process and, consequently, binder hops to
handle /dev/ashmem results in performance/memory overhead.

To address the overhead, replace ashmemd with a duplicate of
/dev/ashmem. Name it /dev/ashmem<boot_id>, where boot_id is a random
number generated on each boot. This way we make sure that developers
don't accidentally depend on /dev/ashmem<boot_id>, as that name can't be
hardcoded.

Bug: 139855428
Test: writing "add"/"remove" to /sys/class/misc/ashmem/uevent correctly
adds/removes /dev/ashmem and /dev/ashmem/boot_id
Change-Id: I36d23116048bfcd99903ba46cc133161835a2cfa
This commit is contained in:
Tri Vo 2019-09-24 13:00:43 -07:00
parent 03642ad8b8
commit ff89b8d8c2
3 changed files with 23 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

21
init/devices.cpp
View file

@ -441,6 +441,23 @@ void DeviceHandler::HandleDevice(const std::string& action, const std::string& d
}
}
void DeviceHandler::HandleAshmemUevent(const Uevent& uevent) {
if (uevent.device_name == "ashmem") {
static const std::string boot_id_path = "/proc/sys/kernel/random/boot_id";
std::string boot_id;
if (!ReadFileToString(boot_id_path, &boot_id)) {
PLOG(ERROR) << "Cannot duplicate ashmem device node. Failed to read " << boot_id_path;
return;
};
boot_id = Trim(boot_id);
Uevent dup_ashmem_uevent = uevent;
dup_ashmem_uevent.device_name += boot_id;
dup_ashmem_uevent.path += boot_id;
HandleUevent(dup_ashmem_uevent);
}
}
void DeviceHandler::HandleUevent(const Uevent& uevent) {
if (uevent.action == "add" || uevent.action == "change" || uevent.action == "online") {
FixupSysPermissions(uevent.path, uevent.subsystem);
@ -485,6 +502,10 @@ void DeviceHandler::HandleUevent(const Uevent& uevent) {
mkdir_recursive(Dirname(devpath), 0755);
HandleDevice(uevent.action, devpath, block, uevent.major, uevent.minor, links);
// Duplicate /dev/ashmem device and name it /dev/ashmem<boot_id>.
// TODO(b/111903542): remove once all users of /dev/ashmem are migrated to libcutils API.
HandleAshmemUevent(uevent);
}
void DeviceHandler::ColdbootDone() {

1
init/devices.h
View file

@ -130,6 +130,7 @@ class DeviceHandler : public UeventHandler {
void HandleDevice(const std::string& action, const std::string& devpath, bool block, int major,
int minor, const std::vector<std::string>& links) const;
void FixupSysPermissions(const std::string& upath, const std::string& subsystem) const;
void HandleAshmemUevent(const Uevent& uevent);
std::vector<Permissions> dev_permissions_;
std::vector<SysfsPermissions> sysfs_permissions_;

2
rootdir/ueventd.rc
View file

@ -33,7 +33,7 @@ subsystem sound
/dev/urandom 0666 root root
# Make HW RNG readable by group system to let EntropyMixer read it.
/dev/hw_random 0440 root system
/dev/ashmem 0666 root root
/dev/ashmem* 0666 root root
/dev/binder 0666 root root
/dev/hwbinder 0666 root root
/dev/vndbinder 0666 root root