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Commit 4bd36874 authored by Jiyong Park's avatar Jiyong Park
Browse files

canned fs_config accepts multiple lines having the same path 

Previously, each file/dir in a filesystem had to have exactly one
matching entry in the canned fs_config file. With this change, the
config file can have multiple entries for the same path. e.g.

/lib/libfoo.so 1000 1000 0644
/lib/libfoo.so 1000 2000 0644 capabilities=0x30

In this case, the last matching entry is chosen and used. This is to
make it possible to customize system-provided (and thus generic)
fs_config file with a user-provided (and thus context-specific) one.

Bug: 209971551
Test: m
Change-Id: I43902fed08db1b4968d02c75fac0a47976fff72a
parent d8602917

libcutils/canned_fs_config.cpp

+20 −11
Original line number Diff line number Diff line
@@ -21,7 +21,6 @@ 
#include <android-base/strings.h>



#include <errno.h>

#include <fnmatch.h>

#include <inttypes.h>

#include <limits.h>

#include <stdio.h>
@@ -67,10 +66,10 @@ int load_canned_fs_config(const char* fn) { 
        }



        // Historical: remove the leading '/' if exists.

        std::string path = tokens[0].front() == '/' ? std::string(tokens[0], 1) : tokens[0];

        std::string path(tokens[0].front() == '/' ? std::string(tokens[0], 1) : tokens[0]);



        Entry e{

                .path = path,

                .path = std::move(path),

                .uid = static_cast<unsigned int>(atoi(tokens[1].c_str())),

                .gid = static_cast<unsigned int>(atoi(tokens[2].c_str())),

                // mode is in octal
@@ -93,8 +92,15 @@ int load_canned_fs_config(const char* fn) { 
        canned_data.emplace_back(std::move(e));

    }



    std::sort(canned_data.begin(), canned_data.end(),

              [](const Entry& a, const Entry& b) -> bool { return a.path < b.path; });

    // Note: we used to sort the entries by path names. This was to improve the lookup performance

    // by doing binary search. However, this is no longer the case. The lookup performance is not

    // critical because this tool runs on the host, not on the device. Now, there can be multiple

    // entries for the same path. Then the one that comes the last wins. This is to allow overriding

    // platform provided fs_config with a user provided fs_config by appending the latter to the

    // former.

    //

    // To implement the strategy, reverse the entries order, and search from the top.

    std::reverse(canned_data.begin(), canned_data.end());



    std::cout << "loaded " << canned_data.size() << " fs_config entries" << std::endl;

    return 0;
@@ -105,12 +111,15 @@ void canned_fs_config(const char* path, [[maybe_unused]] int dir, 
                      unsigned* mode, uint64_t* capabilities) {

    if (path != nullptr && path[0] == '/') path++;  // canned paths lack the leading '/'



    const Entry* found = static_cast<Entry*>(

            bsearch(path, &canned_data[0], canned_data.size(), sizeof(Entry),

                    [](const void* a, const void* b) -> int {

                        return strcmp(static_cast<const char*>(a),

                                      static_cast<const Entry*>(b)->path.c_str());

                    }));

    const Entry* found = nullptr;

    // canned_data is already reversed. First match wins.

    for (const auto& entry : canned_data) {

        if (path == entry.path) {

            found = &entry;

            break;

        }

        continue;

    }



    if (found == nullptr) {

        std::cerr << "failed to find " << path << " in canned fs_config" << std::endl;