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Commit 62aeb16e authored by Mark Salyzyn's avatar Mark Salyzyn
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fs_mgr: overlayfs skip mount points that are more specific 

This is an optimization to limit us to an optimal set of overlay
mounts.  If an entry is identical or more specific (eg: /vendor is
less specific than /vendor/firmware_file), then no need to craft an
override for it.

We do the check in the setup and mount_all paths.

Test: confirm on devices with more specific mounts they do not get override
Bug: 109821005
Change-Id: If34775455fc7989903f70bc4f075c948db91ce37
parent 065cdf32

fs_mgr/fs_mgr_overlayfs.cpp

+32 −18
Original line number Diff line number Diff line
@@ -360,6 +360,34 @@ bool fs_mgr_overlayfs_already_mounted(const std::string& mount_point) { 
    return false;

}



std::vector<std::string> fs_mgr_candidate_list(const fstab* fstab,

                                               const char* mount_point = nullptr) {

    std::vector<std::string> mounts;

    if (!fstab) return mounts;



    for (auto i = 0; i < fstab->num_entries; i++) {

        const auto fsrec = &fstab->recs[i];

        if (!fs_mgr_wants_overlayfs(fsrec)) continue;

        std::string new_mount_point(fs_mgr_mount_point(fstab, fsrec->mount_point));

        if (mount_point && (new_mount_point != mount_point)) continue;

        auto duplicate_or_more_specific = false;

        for (auto it = mounts.begin(); it != mounts.end();) {

            if ((*it == new_mount_point) ||

                (android::base::StartsWith(new_mount_point, *it + "/"))) {

                duplicate_or_more_specific = true;

                break;

            }

            if (android::base::StartsWith(*it, new_mount_point + "/")) {

                it = mounts.erase(it);

            } else {

                ++it;

            }

        }

        if (!duplicate_or_more_specific) mounts.emplace_back(new_mount_point);

    }

    return mounts;

}



}  // namespace



bool fs_mgr_overlayfs_mount_all() {
@@ -371,10 +399,7 @@ bool fs_mgr_overlayfs_mount_all() { 
                                                                      fs_mgr_free_fstab);

    if (!fstab) return ret;



    for (auto i = 0; i < fstab->num_entries; i++) {

        const auto fsrec = &fstab->recs[i];

        if (!fs_mgr_wants_overlayfs(fsrec)) continue;

        std::string mount_point(fs_mgr_mount_point(fstab.get(), fsrec->mount_point));

    for (const auto& mount_point : fs_mgr_candidate_list(fstab.get())) {

        if (fs_mgr_overlayfs_already_mounted(mount_point)) continue;

        if (fs_mgr_overlayfs_mount(mount_point)) ret = true;

    }
@@ -399,20 +424,9 @@ bool fs_mgr_overlayfs_setup(const char* backing, const char* mount_point, bool* 


    std::unique_ptr<struct fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab_default(),

                                                                      fs_mgr_free_fstab);

    std::vector<std::string> mounts;

    mount_point = fs_mgr_mount_point(fstab.get(), mount_point);

    if (fstab) {

        if (!fs_mgr_get_entry_for_mount_point(fstab.get(), kOverlayMountPoint)) return ret;

        for (auto i = 0; i < fstab->num_entries; i++) {

            const auto fsrec = &fstab->recs[i];

            auto fsrec_mount_point = fs_mgr_mount_point(fstab.get(), fsrec->mount_point);

            if (!fsrec_mount_point) continue;

            if (mount_point && strcmp(fsrec_mount_point, mount_point)) continue;

            if (!fs_mgr_wants_overlayfs(fsrec)) continue;

            mounts.emplace_back(fsrec_mount_point);

        }

        if (mounts.empty()) return ret;

    }

    if (fstab && !fs_mgr_get_entry_for_mount_point(fstab.get(), kOverlayMountPoint)) return ret;

    auto mounts = fs_mgr_candidate_list(fstab.get(), fs_mgr_mount_point(fstab.get(), mount_point));

    if (fstab && mounts.empty()) return ret;



    auto overlay = kOverlayMountPoint + "/overlay/";

    auto save_errno = errno;