Merge "COW device initialized by zeroing the whole first chunk"

#include <android-base/strings.h>

#include <fs_mgr/roots.h>

using android::dm::kSectorSize;

using android::fs_mgr::EnsurePathMounted;

using android::fs_mgr::EnsurePathUnmounted;

using android::fs_mgr::Fstab;

    // so it can be used to resume the last state of a snapshot device;

    // - an _INVALID_ snapshot otherwise.

    // To avoid zero-filling the whole CoW file when a new dm-snapshot is

    // created, here we zero-fill only the first 32 bits. This is a temporary

    // workaround that will be discussed again when the kernel API gets

    // consolidated.

    // TODO(b/139202197): Remove this hack once the kernel API is consolidated.

    constexpr ssize_t kDmSnapZeroFillSize = 4;  // 32-bit

    // created, here we zero-fill only the first chunk to be compliant with

    // lvm.

    constexpr ssize_t kDmSnapZeroFillSize = kSectorSize * kSnapshotChunkSize;

    char zeros[kDmSnapZeroFillSize] = {0};

    std::vector<uint8_t> zeros(kDmSnapZeroFillSize, 0);

    android::base::unique_fd fd(open(device.c_str(), O_WRONLY | O_BINARY));

    if (fd < 0) {

        PLOG(ERROR) << "Can't open COW device: " << device;

    }

    LOG(INFO) << "Zero-filling COW device: " << device;

    if (!android::base::WriteFully(fd, zeros, kDmSnapZeroFillSize)) {

    if (!android::base::WriteFully(fd, zeros.data(), kDmSnapZeroFillSize)) {

        PLOG(ERROR) << "Can't zero-fill COW device for " << device;

        return false;

    }