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COW device initialized by zeroing the whole first chunk 

To be compliant with lvm, instead of just zeroing the first 32 bit of
the COW device, force to zero the whole first chunk.
Also switch to std::vector to store the zeroes, reducing the stack
growth.

Test: libsnapshot_test
Bug: 139202197
Change-Id: I2d98549528a222d6c27bb566c68477b5ec3add20
Signed-off-by: Alessio Balsini <balsini@google.com>
This commit is contained in:
Alessio Balsini 2019-10-30 17:28:24 +00:00
parent e901d3a3ee
commit 3ab9f1f85b
1 changed files with 6 additions and 7 deletions
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13
fs_mgr/libsnapshot/utility.cpp
View File

@ -19,6 +19,7 @@
#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;
@ -94,13 +95,11 @@ bool InitializeCow(const std::string& device) {
// 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;
@ -108,7 +107,7 @@ bool InitializeCow(const std::string& 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;
}