<commit_before>#include "globals.hh"
#include "misc.hh"
#include "local-store.hh"

#include <boost/shared_ptr.hpp>

#include <functional>
#include <queue>
#include <algorithm>

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>


namespace nix {


static string gcLockName = "gc.lock";
static string tempRootsDir = "temproots";
static string gcRootsDir = "gcroots";

static const int defaultGcLevel = 1000;


/* Acquire the global GC lock.  This is used to prevent new Nix
   processes from starting after the temporary root files have been
   read.  To be precise: when they try to create a new temporary root
   file, they will block until the garbage collector has finished /
   yielded the GC lock. */
int LocalStore::openGCLock(LockType lockType)
{
    Path fnGCLock = (format("%1%/%2%")
        % nixStateDir % gcLockName).str();
         
    debug(format("acquiring global GC lock `%1%'") % fnGCLock);
    
    AutoCloseFD fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT, 0600);
    if (fdGCLock == -1)
        throw SysError(format("opening global GC lock `%1%'") % fnGCLock);

    if (!lockFile(fdGCLock, lockType, false)) {
        printMsg(lvlError, format("waiting for the big garbage collector lock..."));
        lockFile(fdGCLock, lockType, true);
    }

    /* !!! Restrict read permission on the GC root.  Otherwise any
       process that can open the file for reading can DoS the
       collector. */
    
    return fdGCLock.borrow();
}


void createSymlink(const Path & link, const Path & target, bool careful)
{
    /* Create directories up to `gcRoot'. */
    createDirs(dirOf(link));

    /* !!! shouldn't removing and creating the symlink be atomic? */

    /* Remove the old symlink. */
    if (pathExists(link)) {
        if (careful && (!isLink(link) || !isInStore(readLink(link))))
            throw Error(format("cannot create symlink `%1%'; already exists") % link);
        unlink(link.c_str());
    }

    /* And create the new one. */
    if (symlink(target.c_str(), link.c_str()) == -1)
        throw SysError(format("symlinking `%1%' to `%2%'")
            % link % target);
}


void LocalStore::syncWithGC()
{
    AutoCloseFD fdGCLock = openGCLock(ltRead);
}


void LocalStore::addIndirectRoot(const Path & path)
{
    string hash = printHash32(hashString(htSHA1, path));
    Path realRoot = canonPath((format("%1%/%2%/auto/%3%")
        % nixStateDir % gcRootsDir % hash).str());
    createSymlink(realRoot, path, false);
}


Path addPermRoot(StoreAPI & store, const Path & _storePath,
    const Path & _gcRoot, bool indirect, bool allowOutsideRootsDir)
{
    Path storePath(canonPath(_storePath));
    Path gcRoot(canonPath(_gcRoot));
    assertStorePath(storePath);

    if (isInStore(gcRoot))
        throw Error(format(
                "creating a garbage collector root (%1%) in the Nix store is forbidden "
                "(are you running nix-build inside the store?)") % gcRoot);

    if (indirect) {
        createSymlink(gcRoot, storePath, true);
        store.addIndirectRoot(gcRoot);
    }

    else {
        if (!allowOutsideRootsDir) {
            Path rootsDir = canonPath((format("%1%/%2%") % nixStateDir % gcRootsDir).str());
    
            if (string(gcRoot, 0, rootsDir.size() + 1) != rootsDir + "/")
                throw Error(format(
                    "path `%1%' is not a valid garbage collector root; "
                    "it's not in the directory `%2%'")
                    % gcRoot % rootsDir);
        }
            
        createSymlink(gcRoot, storePath, false);
    }

    /* Check that the root can be found by the garbage collector.
       !!! This can be very slow on machines that have many roots.
       Instead of reading all the roots, it would be more efficient to
       check if the root is in a directory in or linked from the
       gcroots directory. */
    if (queryBoolSetting("gc-check-reachability", false)) {
        Roots roots = store.findRoots();
        if (roots.find(gcRoot) == roots.end())
            printMsg(lvlError, 
                format(
                    "warning: `%1%' is not in a directory where the garbage collector looks for roots; "
                    "therefore, `%2%' might be removed by the garbage collector")
                % gcRoot % storePath);
    }

    /* Grab the global GC root, causing us to block while a GC is in
       progress.  This prevents the set of permanent roots from
       increasing while a GC is in progress. */
    store.syncWithGC();
    
    return gcRoot;
}


/* The file to which we write our temporary roots. */
static Path fnTempRoots;
static AutoCloseFD fdTempRoots;


void LocalStore::addTempRoot(const Path & path)
{
    /* Create the temporary roots file for this process. */
    if (fdTempRoots == -1) {

        while (1) {
            Path dir = (format("%1%/%2%") % nixStateDir % tempRootsDir).str();
            createDirs(dir);
            
            fnTempRoots = (format("%1%/%2%")
                % dir % getpid()).str();

            AutoCloseFD fdGCLock = openGCLock(ltRead);
            
            if (pathExists(fnTempRoots))
                /* It *must* be stale, since there can be no two
                   processes with the same pid. */
                deletePath(fnTempRoots);

	    fdTempRoots = openLockFile(fnTempRoots, true);

            fdGCLock.close();
      
            debug(format("acquiring read lock on `%1%'") % fnTempRoots);
            lockFile(fdTempRoots, ltRead, true);

            /* Check whether the garbage collector didn't get in our
               way. */
            struct stat st;
            if (fstat(fdTempRoots, &st) == -1)
                throw SysError(format("statting `%1%'") % fnTempRoots);
            if (st.st_size == 0) break;
            
            /* The garbage collector deleted this file before we could
               get a lock.  (It won't delete the file after we get a
               lock.)  Try again. */
        }<commit_msg>Don't use deletePath() to delete a single file<commit_after>#include "globals.hh"
#include "misc.hh"
#include "local-store.hh"

#include <boost/shared_ptr.hpp>

#include <functional>
#include <queue>
#include <algorithm>

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>


namespace nix {


static string gcLockName = "gc.lock";
static string tempRootsDir = "temproots";
static string gcRootsDir = "gcroots";

static const int defaultGcLevel = 1000;


/* Acquire the global GC lock.  This is used to prevent new Nix
   processes from starting after the temporary root files have been
   read.  To be precise: when they try to create a new temporary root
   file, they will block until the garbage collector has finished /
   yielded the GC lock. */
int LocalStore::openGCLock(LockType lockType)
{
    Path fnGCLock = (format("%1%/%2%")
        % nixStateDir % gcLockName).str();
         
    debug(format("acquiring global GC lock `%1%'") % fnGCLock);
    
    AutoCloseFD fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT, 0600);
    if (fdGCLock == -1)
        throw SysError(format("opening global GC lock `%1%'") % fnGCLock);

    if (!lockFile(fdGCLock, lockType, false)) {
        printMsg(lvlError, format("waiting for the big garbage collector lock..."));
        lockFile(fdGCLock, lockType, true);
    }

    /* !!! Restrict read permission on the GC root.  Otherwise any
       process that can open the file for reading can DoS the
       collector. */
    
    return fdGCLock.borrow();
}


void createSymlink(const Path & link, const Path & target, bool careful)
{
    /* Create directories up to `gcRoot'. */
    createDirs(dirOf(link));

    /* !!! shouldn't removing and creating the symlink be atomic? */

    /* Remove the old symlink. */
    if (pathExists(link)) {
        if (careful && (!isLink(link) || !isInStore(readLink(link))))
            throw Error(format("cannot create symlink `%1%'; already exists") % link);
        unlink(link.c_str());
    }

    /* And create the new one. */
    if (symlink(target.c_str(), link.c_str()) == -1)
        throw SysError(format("symlinking `%1%' to `%2%'")
            % link % target);
}


void LocalStore::syncWithGC()
{
    AutoCloseFD fdGCLock = openGCLock(ltRead);
}


void LocalStore::addIndirectRoot(const Path & path)
{
    string hash = printHash32(hashString(htSHA1, path));
    Path realRoot = canonPath((format("%1%/%2%/auto/%3%")
        % nixStateDir % gcRootsDir % hash).str());
    createSymlink(realRoot, path, false);
}


Path addPermRoot(StoreAPI & store, const Path & _storePath,
    const Path & _gcRoot, bool indirect, bool allowOutsideRootsDir)
{
    Path storePath(canonPath(_storePath));
    Path gcRoot(canonPath(_gcRoot));
    assertStorePath(storePath);

    if (isInStore(gcRoot))
        throw Error(format(
                "creating a garbage collector root (%1%) in the Nix store is forbidden "
                "(are you running nix-build inside the store?)") % gcRoot);

    if (indirect) {
        createSymlink(gcRoot, storePath, true);
        store.addIndirectRoot(gcRoot);
    }

    else {
        if (!allowOutsideRootsDir) {
            Path rootsDir = canonPath((format("%1%/%2%") % nixStateDir % gcRootsDir).str());
    
            if (string(gcRoot, 0, rootsDir.size() + 1) != rootsDir + "/")
                throw Error(format(
                    "path `%1%' is not a valid garbage collector root; "
                    "it's not in the directory `%2%'")
                    % gcRoot % rootsDir);
        }
            
        createSymlink(gcRoot, storePath, false);
    }

    /* Check that the root can be found by the garbage collector.
       !!! This can be very slow on machines that have many roots.
       Instead of reading all the roots, it would be more efficient to
       check if the root is in a directory in or linked from the
       gcroots directory. */
    if (queryBoolSetting("gc-check-reachability", false)) {
        Roots roots = store.findRoots();
        if (roots.find(gcRoot) == roots.end())
            printMsg(lvlError, 
                format(
                    "warning: `%1%' is not in a directory where the garbage collector looks for roots; "
                    "therefore, `%2%' might be removed by the garbage collector")
                % gcRoot % storePath);
    }

    /* Grab the global GC root, causing us to block while a GC is in
       progress.  This prevents the set of permanent roots from
       increasing while a GC is in progress. */
    store.syncWithGC();
    
    return gcRoot;
}


/* The file to which we write our temporary roots. */
static Path fnTempRoots;
static AutoCloseFD fdTempRoots;


void LocalStore::addTempRoot(const Path & path)
{
    /* Create the temporary roots file for this process. */
    if (fdTempRoots == -1) {

        while (1) {
            Path dir = (format("%1%/%2%") % nixStateDir % tempRootsDir).str();
            createDirs(dir);
            
            fnTempRoots = (format("%1%/%2%")
                % dir % getpid()).str();

            AutoCloseFD fdGCLock = openGCLock(ltRead);
            
            if (pathExists(fnTempRoots))
                /* It *must* be stale, since there can be no two
                   processes with the same pid. */
                unlink(fnTempRoots.c_str());

	    fdTempRoots = openLockFile(fnTempRoots, true);

            fdGCLock.close();
      
            debug(format("acquiring read lock on `%1%'") % fnTempRoots);
            lockFile(fdTempRoots, ltRead, true);

            /* Check whether the garbage collector didn't get in our
               way. */
            struct stat st;
            if (fstat(fdTempRoots, &st) == -1)
                throw SysError(format("statting `%1%'") % fnTempRoots);
            if (st.st_size == 0) break;
            
            /* The garbage collector deleted this file before we could
               get a lock.  (It won't delete the file after we get a
               lock.)  Try again. */
        }
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