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Commit fc592327 authored by Daniel Rosenberg's avatar Daniel Rosenberg
Browse files

Switch sdcardfs over to bind mounts. 

Sdcardfs has been modified to use bind mounts
in place of three separate mounts. This lowers
resource usage, and removes a number of race
conditions around updates via differnt views.

Test: Run storage cts tests with sdcardfs enabled
Change-Id: Icdc196ba3d6f46d54d27ef91c01ffebcf81dd47e
parent 16017b3f

sdcard/sdcard.cpp

+25 −5
Original line number Diff line number Diff line
@@ -331,6 +331,27 @@ static bool sdcardfs_setup(const std::string& source_path, const std::string& de 
    return true;

}



static bool sdcardfs_setup_bind_remount(const std::string& source_path, const std::string& dest_path,

                                        gid_t gid, mode_t mask) {

    std::string opts = android::base::StringPrintf("mask=%d,gid=%d", mask, gid);



    if (mount(source_path.c_str(), dest_path.c_str(), nullptr,

            MS_BIND, nullptr) != 0) {

        PLOG(ERROR) << "failed to bind mount sdcardfs filesystem";

        return false;

    }



    if (mount(source_path.c_str(), dest_path.c_str(), "none",

            MS_REMOUNT | MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_NOATIME, opts.c_str()) != 0) {

        PLOG(ERROR) << "failed to mount sdcardfs filesystem";

        if (umount2(dest_path.c_str(), MNT_DETACH))

            PLOG(WARNING) << "Failed to unmount bind";

        return false;

    }



    return true;

}



static void run_sdcardfs(const std::string& source_path, const std::string& label, uid_t uid,

        gid_t gid, userid_t userid, bool multi_user, bool full_write) {

    std::string dest_path_default = "/mnt/runtime/default/" + label;
@@ -343,9 +364,8 @@ static void run_sdcardfs(const std::string& source_path, const std::string& labe 
        // permissions are completely masked off.

        if (!sdcardfs_setup(source_path, dest_path_default, uid, gid, multi_user, userid,

                                                      AID_SDCARD_RW, 0006)

                || !sdcardfs_setup(source_path, dest_path_read, uid, gid, multi_user, userid,

                                                      AID_EVERYBODY, 0027)

                || !sdcardfs_setup(source_path, dest_path_write, uid, gid, multi_user, userid,

                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_read, AID_EVERYBODY, 0027)

                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_write,

                                                      AID_EVERYBODY, full_write ? 0007 : 0027)) {

            LOG(FATAL) << "failed to sdcardfs_setup";

        }
@@ -355,9 +375,9 @@ static void run_sdcardfs(const std::string& source_path, const std::string& labe 
        // deep inside attr_from_stat().

        if (!sdcardfs_setup(source_path, dest_path_default, uid, gid, multi_user, userid,

                                                      AID_SDCARD_RW, 0006)

                || !sdcardfs_setup(source_path, dest_path_read, uid, gid, multi_user, userid,

                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_read,

                                                      AID_EVERYBODY, full_write ? 0027 : 0022)

                || !sdcardfs_setup(source_path, dest_path_write, uid, gid, multi_user, userid,

                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_write,

                                                      AID_EVERYBODY, full_write ? 0007 : 0022)) {

            LOG(FATAL) << "failed to sdcardfs_setup";

        }