MmappedFile.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 47    Store Directory Routines */
 
#include "squid.h"
#include "debug/Stream.h"
#include "DiskIO/IORequestor.h"
#include "DiskIO/Mmapped/MmappedFile.h"
#include "DiskIO/ReadRequest.h"
#include "DiskIO/WriteRequest.h"
#include "fs_io.h"
#include "globals.h"
 
#include <cerrno>
#if HAVE_SYS_MMAN_H
#include <sys/mman.h>
#endif
#if HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
 
// Some systems such as Hurd provide mmap() API but do not support MAP_NORESERVE
#ifndef MAP_NORESERVE
#define MAP_NORESERVE 0
#endif
 
CBDATA_CLASS_INIT(MmappedFile);
 
// helper class to deal with mmap(2) offset alignment and other low-level specs
class Mmapping
{
public:
    Mmapping(int fd, size_t length, int prot, int flags, off_t offset);
    ~Mmapping();
 
    void *map(); 
    bool unmap(); 
 
private:
    const int fd; 
    const size_t length; 
    const int prot; 
    const int flags; 
    const off_t offset; 
 
    off_t delta; 
    void *buf; 
};
 
MmappedFile::MmappedFile(char const *aPath): fd(-1),
    minOffset(0), maxOffset(-1), error_(false)
{
    assert(aPath);
    path_ = xstrdup(aPath);
    debugs(79,5, this << ' ' << path_);
}
 
MmappedFile::~MmappedFile()
{
    safe_free(path_);
    doClose();
}
 
// XXX: almost a copy of BlockingFile::open
void
MmappedFile::open(int flags, mode_t, RefCount<IORequestor> callback)
{
    assert(fd < 0);
 
    /* Simulate async calls */
    fd = file_open(path_, flags);
    ioRequestor = callback;
 
    if (fd < 0) {
        int xerrno = errno;
        debugs(79,3, "open error: " << xstrerr(xerrno));
        error_ = true;
    } else {
        ++store_open_disk_fd;
        debugs(79,3, "FD " << fd);
 
        // setup mapping boundaries
        struct stat sb;
        if (fstat(fd, &sb) == 0)
            maxOffset = sb.st_size; // we do not expect it to change
    }
 
    callback->ioCompletedNotification();
}
 
void
MmappedFile::create(int flags, mode_t mode, RefCount<IORequestor> callback)
{
    /* We use the same logic path for open */
    open(flags, mode, callback);
}
 
void MmappedFile::doClose()
{
    if (fd >= 0) {
        file_close(fd);
        fd = -1;
        --store_open_disk_fd;
    }
}
 
void
MmappedFile::close()
{
    debugs(79, 3, this << " closing for " << ioRequestor);
    doClose();
    assert(ioRequestor != nullptr);
    ioRequestor->closeCompleted();
}
 
bool
MmappedFile::canRead() const
{
    return fd >= 0;
}
 
bool
MmappedFile::canWrite() const
{
    return fd >= 0;
}
 
bool
MmappedFile::error() const
{
    return error_;
}
 
void
MmappedFile::read(ReadRequest *aRequest)
{
    debugs(79,3, "(FD " << fd << ", " << aRequest->len << ", " <<
           aRequest->offset << ")");
 
    assert(fd >= 0);
    assert(ioRequestor != nullptr);
    assert(aRequest->len > 0); // TODO: work around mmap failures on zero-len?
    assert(aRequest->offset >= 0);
    assert(!error_); // TODO: propagate instead?
 
    assert(minOffset < 0 || minOffset <= aRequest->offset);
    assert(maxOffset < 0 || static_cast<uint64_t>(aRequest->offset + aRequest->len) <= static_cast<uint64_t>(maxOffset));
 
    Mmapping mapping(fd, aRequest->len, PROT_READ, MAP_PRIVATE | MAP_NORESERVE,
                     aRequest->offset);
 
    bool done = false;
    if (void *buf = mapping.map()) {
        memcpy(aRequest->buf, buf, aRequest->len);
        done = mapping.unmap();
    }
    error_ = !done;
 
    const ssize_t rlen = error_ ? -1 : (ssize_t)aRequest->len;
    const int errflag = error_ ? DISK_ERROR :DISK_OK;
    ioRequestor->readCompleted(aRequest->buf, rlen, errflag, aRequest);
}
 
void
MmappedFile::write(WriteRequest *aRequest)
{
    debugs(79,3, "(FD " << fd << ", " << aRequest->len << ", " <<
           aRequest->offset << ")");
 
    assert(fd >= 0);
    assert(ioRequestor != nullptr);
    assert(aRequest->len > 0); // TODO: work around mmap failures on zero-len?
    assert(aRequest->offset >= 0);
    assert(!error_); // TODO: propagate instead?
 
    assert(minOffset < 0 || minOffset <= aRequest->offset);
    assert(maxOffset < 0 || static_cast<uint64_t>(aRequest->offset + aRequest->len) <= static_cast<uint64_t>(maxOffset));
 
    const ssize_t written =
        pwrite(fd, aRequest->buf, aRequest->len, aRequest->offset);
    if (written < 0) {
        debugs(79, DBG_IMPORTANT, "ERROR: " << xstrerr(errno));
        error_ = true;
    } else if (static_cast<size_t>(written) != aRequest->len) {
        debugs(79, DBG_IMPORTANT, "problem: " << written << " < " << aRequest->len);
        error_ = true;
    }
 
    if (aRequest->free_func)
        (aRequest->free_func)(const_cast<char*>(aRequest->buf)); // broken API?
 
    if (!error_) {
        debugs(79,5, "wrote " << aRequest->len << " to FD " << fd << " at " << aRequest->offset);
    } else {
        doClose();
    }
 
    const ssize_t rlen = error_ ? 0 : (ssize_t)aRequest->len;
    const int errflag = error_ ? DISK_ERROR :DISK_OK;
    ioRequestor->writeCompleted(errflag, rlen, aRequest);
}
 
bool
MmappedFile::ioInProgress() const
{
    return false;
}
 
Mmapping::Mmapping(int aFd, size_t aLength, int aProt, int aFlags, off_t anOffset):
    fd(aFd), length(aLength), prot(aProt), flags(aFlags), offset(anOffset),
    delta(-1), buf(nullptr)
{
}
 
Mmapping::~Mmapping()
{
    if (buf)
        unmap();
}
 
void *
Mmapping::map()
{
    // mmap(2) requires that offset is a multiple of the page size
    static const int pageSize = getpagesize();
    delta = offset % pageSize;
 
    buf = mmap(nullptr, length + delta, prot, flags, fd, offset - delta);
 
    if (buf == MAP_FAILED) {
        const int errNo = errno;
        debugs(79,3, "error FD " << fd << "mmap(" << length << '+' <<
               delta << ", " << offset << '-' << delta << "): " << xstrerr(errNo));
        buf = nullptr;
        return nullptr;
    }
 
    return static_cast<char*>(buf) + delta;
}
 
bool
Mmapping::unmap()
{
    debugs(79,9, "FD " << fd <<
           " munmap(" << buf << ", " << length << '+' << delta << ')');
 
    if (!buf) // forgot or failed to map
        return false;
 
    const bool error = munmap(buf, length + delta) != 0;
    if (error) {
        const int errNo = errno;
        debugs(79,3, "error FD " << fd <<
               " munmap(" << buf << ", " << length << '+' << delta << "): " <<
               "): " << xstrerr(errNo));
    }
    buf = nullptr;
    return !error;
}
 
// TODO: check MAP_NORESERVE, consider MAP_POPULATE and MAP_FIXED