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libdm: Make ExtractBlockDeviceName() return its result

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From https://engdoc.corp.google.com/eng/doc/devguide/cpp/styleguide.md:
"Prefer using return values over output parameters: they improve
readability, and often provide the same or better performance (see the C++
Primer)." Implement this advice for ExtractBlockDeviceName(). This patch
does not change any functionality.

Bug: 194450129
Test: mm libfs_mgr libdm_test
Change-Id: I6363781163eba08e6128507b403200f472f68a59
Signed-off-by: Bart Van Assche <bvanassche@google.com>
This commit is contained in:
Bart Van Assche 2021-08-12 10:56:44 -07:00
parent c5c532fc31
commit 6b296db8e3
1 changed files with 13 additions and 17 deletions
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30
fs_mgr/libdm/dm.cpp
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@ -578,34 +578,30 @@ std::string DeviceMapper::GetTargetType(const struct dm_target_spec& spec) {
return std::string{spec.target_type, sizeof(spec.target_type)};
}
static bool ExtractBlockDeviceName(const std::string& path, std::string* name) {
static std::optional<std::string> ExtractBlockDeviceName(const std::string& path) {
static constexpr std::string_view kDevBlockPrefix("/dev/block/");
if (android::base::StartsWith(path, kDevBlockPrefix)) {
*name = path.substr(kDevBlockPrefix.length());
return true;
return path.substr(kDevBlockPrefix.length());
}
return false;
return {};
}
bool DeviceMapper::IsDmBlockDevice(const std::string& path) {
std::string name;
if (!ExtractBlockDeviceName(path, &name)) {
return false;
}
return android::base::StartsWith(name, "dm-");
std::optional<std::string> name = ExtractBlockDeviceName(path);
return name && android::base::StartsWith(*name, "dm-");
}
std::optional<std::string> DeviceMapper::GetDmDeviceNameByPath(const std::string& path) {
std::string name;
if (!ExtractBlockDeviceName(path, &name)) {
std::optional<std::string> name = ExtractBlockDeviceName(path);
if (!name) {
LOG(WARNING) << path << " is not a block device";
return std::nullopt;
}
if (!android::base::StartsWith(name, "dm-")) {
if (!android::base::StartsWith(*name, "dm-")) {
LOG(WARNING) << path << " is not a dm device";
return std::nullopt;
}
std::string dm_name_file = "/sys/block/" + name + "/dm/name";
std::string dm_name_file = "/sys/block/" + *name + "/dm/name";
std::string dm_name;
if (!android::base::ReadFileToString(dm_name_file, &dm_name)) {
PLOG(ERROR) << "Failed to read file " << dm_name_file;
@ -616,16 +612,16 @@ std::optional<std::string> DeviceMapper::GetDmDeviceNameByPath(const std::string
}
std::optional<std::string> DeviceMapper::GetParentBlockDeviceByPath(const std::string& path) {
std::string name;
if (!ExtractBlockDeviceName(path, &name)) {
std::optional<std::string> name = ExtractBlockDeviceName(path);
if (!name) {
LOG(WARNING) << path << " is not a block device";
return std::nullopt;
}
if (!android::base::StartsWith(name, "dm-")) {
if (!android::base::StartsWith(*name, "dm-")) {
// Reached bottom of the device mapper stack.
return std::nullopt;
}
auto slaves_dir = "/sys/block/" + name + "/slaves";
auto slaves_dir = "/sys/block/" + *name + "/slaves";
auto dir = std::unique_ptr<DIR, decltype(&closedir)>(opendir(slaves_dir.c_str()), closedir);
if (dir == nullptr) {
PLOG(ERROR) << "Failed to open: " << slaves_dir;