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Commit 63740b96 authored by Siarhei Vishniakou's avatar Siarhei Vishniakou
Browse files

Use getrandom for device input event ID generation 

On device, let's go back to using 'getrandom' for the generation of
random input event ids. This should be faster than reading from
/dev/urandom.

This is a partial revert of the previous patch. After this patch, we
will only use '/dev/urandom' on host.

We may be able to switch to 'getrandom' for both if we ever switch to
musl for host. We can revisit it then.

Bug: 254215895
Test: m &&  atest --host libinput_tests
Change-Id: Idc6241facbd93f3f71ae90567db831d96a5fc98b
parent 6eafa9dd

libs/input/Input.cpp

+24 −2
Original line number Diff line number Diff line
@@ -35,6 +35,9 @@ 
#ifdef __linux__

#include <binder/Parcel.h>

#endif

#if defined(__ANDROID__)

#include <sys/random.h>

#endif



using android::base::StringPrintf;
@@ -110,8 +113,11 @@ const char* motionToolTypeToString(int32_t toolType) { 
}



// --- IdGenerator ---



static status_t getRandomBytes(uint8_t* data, size_t size) {

#if defined(__ANDROID__)

[[maybe_unused]]

#endif

static status_t

getRandomBytes(uint8_t* data, size_t size) {

    int ret = TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY | O_CLOEXEC | O_NOFOLLOW));

    if (ret == -1) {

        return -errno;
@@ -130,7 +136,22 @@ int32_t IdGenerator::nextId() const { 
    constexpr uint32_t SEQUENCE_NUMBER_MASK = ~SOURCE_MASK;

    int32_t id = 0;



#if defined(__ANDROID__)

    // On device, prefer 'getrandom' to '/dev/urandom' because it's faster.

    constexpr size_t BUF_LEN = sizeof(id);

    size_t totalBytes = 0;

    while (totalBytes < BUF_LEN) {

        ssize_t bytes = TEMP_FAILURE_RETRY(getrandom(&id, BUF_LEN, GRND_NONBLOCK));

        if (CC_UNLIKELY(bytes < 0)) {

            ALOGW("Failed to fill in random number for sequence number: %s.", strerror(errno));

            id = 0;

            break;

        }

        totalBytes += bytes;

    }

#else

#if defined(__linux__)

    // On host, <sys/random.h> / GRND_NONBLOCK is not available

    while (true) {

        status_t result = getRandomBytes(reinterpret_cast<uint8_t*>(&id), sizeof(id));

        if (result == OK) {
@@ -138,6 +159,7 @@ int32_t IdGenerator::nextId() const { 
        }

    }

#endif // __linux__

#endif // __ANDROID__

    return (id & SEQUENCE_NUMBER_MASK) | static_cast<int32_t>(mSource);

}