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Commit 912b9d06 authored by Jooyung Han's avatar Jooyung Han
Browse files

libdm: LoopControl::Add/Remove(id) 

This new methods wraps ioctl(LOOP_CTL_ADD/LOOP_CTL_REMOVE) with a given
ID.

Bug: 413174275
Flag: com.android.apex.flags.mount_before_data
Test: libdm_test
Change-Id: Id8b95180771590ac10e207212a80bd08f30d95d8
parent 39b0bac0

fs_mgr/libdm/include/libdm/loop_control.h

+8 −0
Original line number Diff line number Diff line
@@ -43,6 +43,12 @@ class LoopControl final { 
    // Detach the loop device given by 'loopdev' from the attached backing file.

    bool Detach(const std::string& loopdev) const;



    // Add a new loop device with given 'id'.

    bool Add(int id) const;



    // Remove the device with given 'id'.

    bool Remove(int id) const;



    // Enable Direct I/O on a loop device. This requires kernel 4.9+.

    static bool EnableDirectIo(int fd);
@@ -60,6 +66,8 @@ class LoopControl final { 
    static constexpr const char* kLoopControlDevice = "/dev/loop-control";



    android::base::unique_fd control_fd_;



    friend struct LoopControlTest;

};



// Create a temporary loop device around a file descriptor or path.

fs_mgr/libdm/loop_control.cpp

+21 −0
Original line number Diff line number Diff line
@@ -98,6 +98,27 @@ bool LoopControl::Detach(const std::string& loopdev) const { 
    return true;

}



bool LoopControl::Add(int id) const {

    int rc = ioctl(control_fd_, LOOP_CTL_ADD, id);

    if (rc < 0) {

        // To avoid logspam

        if (errno != EEXIST) {

            PLOG(ERROR) << "Failed LOOP_CTL_ADD to add a loop device " << id;

        }

        return false;

    }

    return true;

}



bool LoopControl::Remove(int id) const {

    int rc = ioctl(control_fd_, LOOP_CTL_REMOVE, id);

    if (rc < 0) {

        PLOG(ERROR) << "Failed LOOP_CTL_REMOVE to remove a loop device " << id;

        return false;

    }

    return true;

}



bool LoopControl::FindFreeLoopDevice(std::string* loopdev) const {

    int rc = ioctl(control_fd_, LOOP_CTL_GET_FREE);

    if (rc < 0) {

fs_mgr/libdm/loop_control_test.cpp

+27 −2
Original line number Diff line number Diff line
@@ -29,8 +29,10 @@ 
#include "test_util.h"



using namespace std;

using namespace android::dm;

using unique_fd = android::base::unique_fd;

using android::base::Basename;

using android::base::unique_fd;



namespace android::dm {



static unique_fd TempFile() {

    // A loop device needs to be at least one sector to actually work, so fill
@@ -62,3 +64,26 @@ TEST(libdm, LoopControl) { 
    ASSERT_TRUE(android::base::ReadFully(loop_fd, buffer, sizeof(buffer)));

    ASSERT_EQ(memcmp(buffer, "Hello", 6), 0);

}



struct LoopControlTest : ::testing::Test {

    LoopControl control;

    // indirection to access private LoopControl::FindFreeLoopDevice() method

    bool FindFreeLoopDevice(std::string* loopdev) const {

        return control.FindFreeLoopDevice(loopdev);

    }

};



TEST_F(LoopControlTest, AddRemove) {

    // Get an id for a free loop device first

    std::string path;

    ASSERT_TRUE(FindFreeLoopDevice(&path));

    std::string name = Basename(path);

    ASSERT_EQ(name.substr(0, 4), "loop");

    int id = atoi(name.substr(4).c_str());



    ASSERT_FALSE(control.Add(id));

    ASSERT_TRUE(control.Remove(id));

    ASSERT_TRUE(control.Add(id));

}



}  // namespace android::dm