Segment.cc

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/*
 * Copyright (C) 1996-2025 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */
 
/* DEBUG: section 54    Interprocess Communication */
 
#include "squid.h"
#include "base/TextException.h"
#include "compat/shm.h"
#include "compat/unistd.h"
#include "debug/Stream.h"
#include "fatal.h"
#include "Instance.h"
#include "ipc/mem/Segment.h"
#include "sbuf/SBuf.h"
#include "SquidConfig.h"
#include "tools.h"
 
#if HAVE_FCNTL_H
#include <fcntl.h>
#endif
#if HAVE_SYS_MMAN_H
#include <sys/mman.h>
#endif
#if HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
 
// test cases change this
const char *Ipc::Mem::Segment::BasePath = DEFAULT_STATEDIR;
 
void *
Ipc::Mem::Segment::reserve(size_t chunkSize)
{
    Must(theMem);
    // check for overflows
    // chunkSize >= 0 may result in warnings on systems where off_t is unsigned
    assert(!chunkSize || static_cast<off_t>(chunkSize) > 0);
    assert(static_cast<off_t>(chunkSize) <= theSize);
    assert(theReserved <= theSize - static_cast<off_t>(chunkSize));
    void *result = reinterpret_cast<char*>(theMem) + theReserved;
    theReserved += chunkSize;
    return result;
}
 
SBuf
Ipc::Mem::Segment::Name(const SBuf &prefix, const char *suffix)
{
    SBuf result = prefix;
    result.append("_");
    result.append(suffix);
    return result;
}
 
#if HAVE_SHM
 
Ipc::Mem::Segment::Segment(const char *const id):
    theFD(-1), theName(GenerateName(id)), theMem(nullptr),
    theSize(0), theReserved(0), doUnlink(false)
{
}
 
Ipc::Mem::Segment::~Segment()
{
    if (theFD >= 0) {
        detach();
        if (xclose(theFD) != 0) {
            int xerrno = errno;
            debugs(54, 5, "close " << theName << ": " << xstrerr(xerrno));
        }
    }
    if (doUnlink)
        unlink();
}
 
// fake Ipc::Mem::Segment::Enabled (!HAVE_SHM) is more selective
bool
Ipc::Mem::Segment::Enabled()
{
    return true;
}
 
void
Ipc::Mem::Segment::create(const off_t aSize)
{
    assert(aSize > 0);
    assert(theFD < 0);
 
    int xerrno = 0;
 
    // Why a brand new segment? A Squid crash may leave a reusable segment, but
    // our placement-new code requires an all-0s segment. We could truncate and
    // resize the old segment, but OS X does not allow using O_TRUNC with
    // shm_open() and does not support ftruncate() for old segments.
    if (!createFresh(xerrno) && xerrno == EEXIST) {
        unlink();
        createFresh(xerrno);
    }
 
    if (theFD < 0) {
        debugs(54, 5, "shm_open " << theName << ": " << xstrerr(xerrno));
        fatalf("Ipc::Mem::Segment::create failed to shm_open(%s): %s\n",
               theName.termedBuf(), xstrerr(xerrno));
    }
 
    if (ftruncate(theFD, aSize)) {
        xerrno = errno;
        unlink();
        debugs(54, 5, "ftruncate " << theName << ": " << xstrerr(xerrno));
        fatalf("Ipc::Mem::Segment::create failed to ftruncate(%s): %s\n",
               theName.termedBuf(), xstrerr(xerrno));
    }
    // We assume that the shm_open(O_CREAT)+ftruncate() combo zeros the segment.
 
    theSize = statSize("Ipc::Mem::Segment::create");
 
    // OS X will round up to a full page, so not checking for exact size match.
    assert(theSize >= aSize);
 
    theReserved = 0;
    doUnlink = true;
 
    debugs(54, 3, "created " << theName << " segment: " << theSize);
    attach();
}
 
void
Ipc::Mem::Segment::open(const bool unlinkWhenDone)
{
    assert(theFD < 0);
 
    theFD = shm_open(theName.termedBuf(), O_RDWR, 0);
    if (theFD < 0) {
        int xerrno = errno;
        debugs(54, 5, "shm_open " << theName << ": " << xstrerr(xerrno));
        fatalf("Ipc::Mem::Segment::open failed to shm_open(%s): %s\n",
               theName.termedBuf(), xstrerr(xerrno));
    }
 
    theSize = statSize("Ipc::Mem::Segment::open");
    doUnlink = unlinkWhenDone;
 
    debugs(54, 3, "opened " << theName << " segment: " << theSize);
 
    attach();
}
 
bool
Ipc::Mem::Segment::createFresh(int &xerrno)
{
    theFD = shm_open(theName.termedBuf(),
                     O_EXCL | O_CREAT | O_RDWR,
                     S_IRUSR | S_IWUSR);
    xerrno = errno;
    return theFD >= 0;
}
 
void
Ipc::Mem::Segment::attach()
{
    assert(theFD >= 0);
    assert(!theMem);
 
    // mmap() accepts size_t for the size; we give it off_t which might
    // be bigger; assert overflows until we support multiple mmap()s?
    assert(theSize == static_cast<off_t>(static_cast<size_t>(theSize)));
 
    void *const p =
        mmap(nullptr, theSize, PROT_READ | PROT_WRITE, MAP_SHARED, theFD, 0);
    if (p == MAP_FAILED) {
        int xerrno = errno;
        debugs(54, 5, "mmap " << theName << ": " << xstrerr(xerrno));
        fatalf("Ipc::Mem::Segment::attach failed to mmap(%s): %s\n",
               theName.termedBuf(), xstrerr(xerrno));
    }
    theMem = p;
 
    lock();
}
 
void
Ipc::Mem::Segment::detach()
{
    if (!theMem)
        return;
 
    if (munmap(theMem, theSize)) {
        int xerrno = errno;
        debugs(54, 5, "munmap " << theName << ": " << xstrerr(xerrno));
        fatalf("Ipc::Mem::Segment::detach failed to munmap(%s): %s\n",
               theName.termedBuf(), xstrerr(xerrno));
    }
    theMem = nullptr;
}
 
void
Ipc::Mem::Segment::lock()
{
    if (!Config.shmLocking) {
        debugs(54, 5, "mlock(2)-ing disabled");
        return;
    }
 
#if defined(_POSIX_MEMLOCK_RANGE)
    debugs(54, 7, "mlock(" << theName << ',' << theSize << ") starts");
    if (mlock(theMem, theSize) != 0) {
        const int savedError = errno;
        fatalf("shared_memory_locking on but failed to mlock(%s, %" PRId64 "): %s\n",
               theName.termedBuf(),static_cast<int64_t>(theSize), xstrerr(savedError));
    }
    // TODO: Warn if it took too long.
    debugs(54, 7, "mlock(" << theName << ',' << theSize << ") OK");
#else
    debugs(54, 5, "insufficient mlock(2) support");
    if (Config.shmLocking.configured()) { // set explicitly
        static bool warnedOnce = false;
        if (!warnedOnce) {
            debugs(54, DBG_IMPORTANT, "ERROR: insufficient mlock(2) support prevents " <<
                   "honoring `shared_memory_locking on`. " <<
                   "If you lack RAM, kernel will kill Squid later.");
            warnedOnce = true;
        }
    }
#endif
}
 
void
Ipc::Mem::Segment::unlink()
{
    if (shm_unlink(theName.termedBuf()) != 0) {
        int xerrno = errno;
        debugs(54, 5, "shm_unlink(" << theName << "): " << xstrerr(xerrno));
    } else
        debugs(54, 3, "unlinked " << theName << " segment");
}
 
off_t
Ipc::Mem::Segment::statSize(const char *context) const
{
    Must(theFD >= 0);
 
    struct stat s;
    memset(&s, 0, sizeof(s));
 
    if (fstat(theFD, &s) != 0) {
        int xerrno = errno;
        debugs(54, 5, context << " fstat " << theName << ": " << xstrerr(xerrno));
        fatalf("Ipc::Mem::Segment::statSize: %s failed to fstat(%s): %s\n",
               context, theName.termedBuf(), xstrerr(xerrno));
    }
 
    return s.st_size;
}
 
String
Ipc::Mem::Segment::GenerateName(const char *id)
{
    assert(BasePath && *BasePath);
    static const bool nameIsPath = shm_portable_segment_name_is_path();
    String name;
    if (nameIsPath) {
        name.append(BasePath);
        if (name[name.size()-1] != '/')
            name.append('/');
    } else {
        name.append(Instance::NamePrefix("/"));
        name.append('-');
    }
 
    // append id, replacing slashes with dots
    for (const char *slash = strchr(id, '/'); slash; slash = strchr(id, '/')) {
        if (id != slash) {
            name.append(id, slash - id);
            name.append('.');
        }
        id = slash + 1;
    }
    name.append(id);
 
    name.append(".shm"); // to distinguish from non-segments when nameIsPath
    return name;
}
 
#else // HAVE_SHM
 
#include <map>
 
typedef std::map<String, Ipc::Mem::Segment *> SegmentMap;
static SegmentMap Segments;
 
Ipc::Mem::Segment::Segment(const char *const id):
    theName(id), theMem(NULL), theSize(0), theReserved(0), doUnlink(false)
{
}
 
Ipc::Mem::Segment::~Segment()
{
    if (doUnlink) {
        delete [] static_cast<char *>(theMem);
        theMem = nullptr;
        Segments.erase(theName);
        debugs(54, 3, "unlinked " << theName << " fake segment");
    }
}
 
bool
Ipc::Mem::Segment::Enabled()
{
    return !UsingSmp() && IamWorkerProcess();
}
 
void
Ipc::Mem::Segment::create(const off_t aSize)
{
    assert(aSize > 0);
    assert(!theMem);
    checkSupport("Fake segment creation");
 
    const bool inserted = Segments.insert(std::make_pair(theName, this)).second;
    if (!inserted)
        fatalf("Duplicate fake segment creation: %s", theName.termedBuf());
 
    theMem = new char[aSize];
    theSize = aSize;
    doUnlink = true;
 
    debugs(54, 3, "created " << theName << " fake segment: " << theSize);
}
 
void
Ipc::Mem::Segment::open(bool)
{
    assert(!theMem);
    checkSupport("Fake segment open");
 
    const SegmentMap::const_iterator i = Segments.find(theName);
    if (i == Segments.end())
        fatalf("Fake segment not found: %s", theName.termedBuf());
 
    const Segment &segment = *i->second;
    theMem = segment.theMem;
    theSize = segment.theSize;
 
    debugs(54, 3, "opened " << theName << " fake segment: " << theSize);
}
 
void
Ipc::Mem::Segment::checkSupport(const char *const context)
{
    if (!Enabled()) {
        debugs(54, 5, context <<
               ": True shared memory segments are not supported. "
               "Cannot fake shared segments in SMP config.");
        fatalf("Ipc::Mem::Segment: Cannot fake shared segments in SMP config (%s)\n",
               context);
    }
}
 
#endif // HAVE_SHM
 
void
Ipc::Mem::RegisteredRunner::useConfig()
{
    // If Squid is built with real segments, we create() real segments
    // in the master process only.  Otherwise, we create() fake
    // segments in each worker process.  We assume that only workers
    // need and can work with fake segments.
#if HAVE_SHM
    if (IamMasterProcess())
#else
    if (IamWorkerProcess())
#endif
        create();
 
    // we assume that master process does not need shared segments
    // unless it is also a worker
    if (!InDaemonMode() || !IamMasterProcess())
        open();
}