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Commit 542aae44 authored by Wei Wang's avatar Wei Wang
Browse files

init: Add readahead built-in command 

Inspired by ag/2659809/, this CL add readahead built-in command in init
to let files be prefetched into pagecache for faster reading.
Readahead happens in background but due to filesystem limitation it
might take small amount of time in it reading the filesystem metadata
needed to locate the requested blocks. So the command is executed in a
forked process to not block init execution.

Bug: 62413151
Test: boottime, dumpcache
Change-Id: I56c86e2ebc20efda4aa509e6efb736bd1d92baa5
parent af6a2620

init/README.md

+3 −0
Original line number Diff line number Diff line
@@ -447,6 +447,9 @@ Commands 
`rmdir <path>`

> Calls rmdir(2) on the given path.



`readahead <file|dir>`

> Calls readahead(2) on the file or files within given directory.



`setprop <name> <value>`

> Set system property _name_ to _value_. Properties are expanded

  within _value_.

init/builtins.cpp

+63 −1
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 
#include <dirent.h>

#include <errno.h>

#include <fcntl.h>

#include <fts.h>

#include <linux/loop.h>

#include <linux/module.h>

#include <mntent.h>
@@ -627,7 +628,7 @@ static int do_rmdir(const std::vector<std::string>& args) { 


static int do_sysclktz(const std::vector<std::string>& args) {

    struct timezone tz = {};

    if (android::base::ParseInt(args[1], &tz.tz_minuteswest) && settimeofday(NULL, &tz) != -1) {

    if (android::base::ParseInt(args[1], &tz.tz_minuteswest) && settimeofday(nullptr, &tz) != -1) {

        return 0;

    }

    return -1;
@@ -660,6 +661,66 @@ static int do_write(const std::vector<std::string>& args) { 
    return 0;

}



static int do_readahead(const std::vector<std::string>& args) {

    struct stat sb;



    if (stat(args[1].c_str(), &sb)) {

        PLOG(ERROR) << "Error opening " << args[1];

        return -1;

    }



    // We will do readahead in a forked process in order not to block init

    // since it may block while it reads the

    // filesystem metadata needed to locate the requested blocks.  This

    // occurs frequently with ext[234] on large files using indirect blocks

    // instead of extents, giving the appearance that the call blocks until

    // the requested data has been read.

    pid_t pid = fork();

    if (pid == 0) {

        android::base::Timer t;

        if (S_ISREG(sb.st_mode)) {

            android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(args[1].c_str(), O_RDONLY)));

            if (fd == -1) {

                PLOG(ERROR) << "Error opening file: " << args[1];

                _exit(EXIT_FAILURE);

            }

            if (readahead(fd, 0, std::numeric_limits<size_t>::max())) {

                PLOG(ERROR) << "Error readahead file: " << args[1];

                _exit(EXIT_FAILURE);

            }

        } else if (S_ISDIR(sb.st_mode)) {

            char* paths[] = {const_cast<char*>(args[1].data()), nullptr};

            std::unique_ptr<FTS, decltype(&fts_close)> fts(

                fts_open(paths, FTS_PHYSICAL | FTS_NOCHDIR | FTS_XDEV, nullptr), fts_close);

            if (!fts) {

                PLOG(ERROR) << "Error opening directory: " << args[1];

                _exit(EXIT_FAILURE);

            }

            // Traverse the entire hierarchy and do readahead

            for (FTSENT* ftsent = fts_read(fts.get()); ftsent != nullptr;

                 ftsent = fts_read(fts.get())) {

                if (ftsent->fts_info & FTS_F) {

                    android::base::unique_fd fd(

                        TEMP_FAILURE_RETRY(open(ftsent->fts_accpath, O_RDONLY)));

                    if (fd == -1) {

                        PLOG(ERROR) << "Error opening file: " << args[1];

                        continue;

                    }

                    if (readahead(fd, 0, std::numeric_limits<size_t>::max())) {

                        PLOG(ERROR) << "Unable to readahead on file: " << ftsent->fts_accpath;

                    }

                }

            }

        }

        LOG(INFO) << "Readahead " << args[1] << " took " << t;

        _exit(0);

    } else if (pid < 0) {

        PLOG(ERROR) << "Fork failed";

        return -1;

    }

    return 0;

}



static int do_copy(const std::vector<std::string>& args) {

    std::string data;

    std::string err;
@@ -898,6 +959,7 @@ const BuiltinFunctionMap::Map& BuiltinFunctionMap::map() const { 
        {"mount_all",               {1,     kMax, do_mount_all}},

        {"mount",                   {3,     kMax, do_mount}},

        {"umount",                  {1,     1,    do_umount}},

        {"readahead",               {1,     1,    do_readahead}},

        {"restart",                 {1,     1,    do_restart}},

        {"restorecon",              {1,     kMax, do_restorecon}},

        {"restorecon_recursive",    {1,     kMax, do_restorecon_recursive}},