commit 2aedc82f021af961fb6f893b299aab25b5529dcf
author Jaegeuk Kim <jaegeuk@google.com> Tue Nov 20 13:27:06 2018 -0800
committer Jaegeuk Kim <jaegeuk@google.com> Tue Jan 15 16:07:59 2019 +0000
tree 74fb5f77292370c979afe6162f6a5d78e12de421
parent 75e6ec7056d3fd14c7ff245abf81d95f64e24fae

zram: support zram_writeback

This patch supports zram_writeback enabled by fstab in two ways.

e.g.,
/dev/block/zram0 none swap defaults
    zramsize=1073741824,max_comp_streams=8,zram_loopback_path=/data/unencrypted/zram_swap

==> loopback size is 512MB by default.

Or,
/dev/block/zram0 none swap defaults
    zramsize=1073741824,max_comp_streams=8,zram_loopback_path=/data/unencrypted/zram_swap,zram_loopback_size=1G

==> loopback size can be specified by "zram_loopback_size=%s" with "GB" or "MB".

Or,
/dev/block/zram0 none swap defaults
    zramsize=1073741824,max_comp_streams=8,zram_backing_dev_path=/dev/block/partition

Bug: 74582279
Bug: 122659265
Change-Id: I66a2e6953b4743a34cf732dd0f5b5256c901f247
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>

init/reboot.cpp

diff --git a/init/reboot.cpp b/init/reboot.cpp
index 45dc6d3..f08d855 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -20,9 +20,11 @@
 #include <fcntl.h>
 #include <linux/fs.h>
 #include <mntent.h>
+#include <linux/loop.h>
 #include <sys/cdefs.h>
 #include <sys/ioctl.h>
 #include <sys/mount.h>
+#include <sys/swap.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
@@ -58,6 +60,7 @@
 using android::base::Split;
 using android::base::StringPrintf;
 using android::base::Timer;
+using android::base::unique_fd;
 
 namespace android {
 namespace init {
@@ -281,6 +284,48 @@
     return stat;
 }
 
+// zram is able to use backing device on top of a loopback device.
+// In order to unmount /data successfully, we have to kill the loopback device first
+#define ZRAM_DEVICE   "/dev/block/zram0"
+#define ZRAM_RESET    "/sys/block/zram0/reset"
+#define ZRAM_BACK_DEV "/sys/block/zram0/backing_dev"
+static void KillZramBackingDevice() {
+    std::string backing_dev;
+    if (!android::base::ReadFileToString(ZRAM_BACK_DEV, &backing_dev)) return;
+
+    if (!android::base::StartsWith(backing_dev, "/dev/block/loop")) return;
+
+    // cut the last "\n"
+    backing_dev.erase(backing_dev.length() - 1);
+
+    // shutdown zram handle
+    Timer swap_timer;
+    LOG(INFO) << "swapoff() start...";
+    if (swapoff(ZRAM_DEVICE) == -1) {
+        LOG(ERROR) << "zram_backing_dev: swapoff (" << backing_dev << ")" << " failed";
+        return;
+    }
+    LOG(INFO) << "swapoff() took " << swap_timer;;
+
+    if (!android::base::WriteStringToFile("1", ZRAM_RESET)) {
+        LOG(ERROR) << "zram_backing_dev: reset (" << backing_dev << ")" << " failed";
+        return;
+    }
+
+    // clear loopback device
+    unique_fd loop(TEMP_FAILURE_RETRY(open(backing_dev.c_str(), O_RDWR | O_CLOEXEC)));
+    if (loop.get() < 0) {
+        LOG(ERROR) << "zram_backing_dev: open(" << backing_dev << ")" << " failed";
+        return;
+    }
+
+    if (ioctl(loop.get(), LOOP_CLR_FD, 0) < 0) {
+        LOG(ERROR) << "zram_backing_dev: loop_clear (" << backing_dev << ")" << " failed";
+        return;
+    }
+    LOG(INFO) << "zram_backing_dev: `" << backing_dev << "` is cleared successfully.";
+}
+
 //* Reboot / shutdown the system.
 // cmd ANDROID_RB_* as defined in android_reboot.h
 // reason Reason string like "reboot", "shutdown,userrequested"
@@ -423,6 +468,9 @@
         sync();
         LOG(INFO) << "sync() before umount took" << sync_timer;
     }
+    // 5. drop caches and disable zram backing device, if exist
+    KillZramBackingDevice();
+
     UmountStat stat = TryUmountAndFsck(runFsck, shutdown_timeout - t.duration());
     // Follow what linux shutdown is doing: one more sync with little bit delay
     {