src/DiskIO/Mmapped/MmappedFile.cc

   1 /*
   2  * Copyright (C) 1996-2020 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 /* DEBUG: section 47    Store Directory Routines */
  10
  11 #include "squid.h"
  12 #include "Debug.h"
  13 #include "DiskIO/IORequestor.h"
  14 #include "DiskIO/Mmapped/MmappedFile.h"
  15 #include "DiskIO/ReadRequest.h"
  16 #include "DiskIO/WriteRequest.h"
  17 #include "fs_io.h"
  18 #include "globals.h"
  19
  20 #include <cerrno>
  21 #if HAVE_SYS_MMAN_H
  22 #include <sys/mman.h>
  23 #endif
  24 #if HAVE_SYS_STAT_H
  25 #include <sys/stat.h>
  26 #endif
  27
  28 // Some systems such as Hurd provide mmap() API but do not support MAP_NORESERVE
  29 #ifndef MAP_NORESERVE
  30 #define MAP_NORESERVE 0
  31 #endif
  32
  33 CBDATA_CLASS_INIT(MmappedFile);
  34
  35 // helper class to deal with mmap(2) offset alignment and other low-level specs
  36 class Mmapping
  37 {
  38 public:
  39     Mmapping(int fd, size_t length, int prot, int flags, off_t offset);
  40     ~Mmapping();
  41
  42     void *map(); ///< calls mmap(2); returns usable buffer or nil on failure
  43     bool unmap(); ///< unmaps previously mapped buffer, if any
  44
  45 private:
  46     const int fd; ///< descriptor of the mmapped file
  47     const size_t length; ///< user-requested data length, needed for munmap
  48     const int prot; ///< mmap(2) "protection" flags
  49     const int flags; ///< other mmap(2) flags
  50     const off_t offset; ///< user-requested data offset
  51
  52     off_t delta; ///< mapped buffer increment to hit user offset
  53     void *buf; ///< buffer returned by mmap, needed for munmap
  54 };
  55
  56 MmappedFile::MmappedFile(char const *aPath): fd(-1),
  57     minOffset(0), maxOffset(-1), error_(false)
  58 {
  59     assert(aPath);
  60     path_ = xstrdup(aPath);
  61     debugs(79,5, HERE << this << ' ' << path_);
  62 }
  63
  64 MmappedFile::~MmappedFile()
  65 {
  66     safe_free(path_);
  67     doClose();
  68 }
  69
  70 // XXX: almost a copy of BlockingFile::open
  71 void
  72 MmappedFile::open(int flags, mode_t, RefCount<IORequestor> callback)
  73 {
  74     assert(fd < 0);
  75
  76     /* Simulate async calls */
  77     fd = file_open(path_, flags);
  78     ioRequestor = callback;
  79
  80     if (fd < 0) {
  81         int xerrno = errno;
  82         debugs(79,3, "open error: " << xstrerr(xerrno));
  83         error_ = true;
  84     } else {
  85         ++store_open_disk_fd;
  86         debugs(79,3, "FD " << fd);
  87
  88         // setup mapping boundaries
  89         struct stat sb;
  90         if (fstat(fd, &sb) == 0)
  91             maxOffset = sb.st_size; // we do not expect it to change
  92     }
  93
  94     callback->ioCompletedNotification();
  95 }
  96
  97 /**
  98  * Alias for MmappedFile::open(...)
  99  \copydoc MmappedFile::open(int flags, mode_t mode, RefCount<IORequestor> callback)
 100  */
 101 void
 102 MmappedFile::create(int flags, mode_t mode, RefCount<IORequestor> callback)
 103 {
 104     /* We use the same logic path for open */
 105     open(flags, mode, callback);
 106 }
 107
 108 void MmappedFile::doClose()
 109 {
 110     if (fd >= 0) {
 111         file_close(fd);
 112         fd = -1;
 113         --store_open_disk_fd;
 114     }
 115 }
 116
 117 void
 118 MmappedFile::close()
 119 {
 120     debugs(79, 3, HERE << this << " closing for " << ioRequestor);
 121     doClose();
 122     assert(ioRequestor != NULL);
 123     ioRequestor->closeCompleted();
 124 }
 125
 126 bool
 127 MmappedFile::canRead() const
 128 {
 129     return fd >= 0;
 130 }
 131
 132 bool
 133 MmappedFile::canWrite() const
 134 {
 135     return fd >= 0;
 136 }
 137
 138 bool
 139 MmappedFile::error() const
 140 {
 141     return error_;
 142 }
 143
 144 void
 145 MmappedFile::read(ReadRequest *aRequest)
 146 {
 147     debugs(79,3, HERE << "(FD " << fd << ", " << aRequest->len << ", " <<
 148            aRequest->offset << ")");
 149
 150     assert(fd >= 0);
 151     assert(ioRequestor != NULL);
 152     assert(aRequest->len > 0); // TODO: work around mmap failures on zero-len?
 153     assert(aRequest->offset >= 0);
 154     assert(!error_); // TODO: propagate instead?
 155
 156     assert(minOffset < 0 || minOffset <= aRequest->offset);
 157     assert(maxOffset < 0 || static_cast<uint64_t>(aRequest->offset + aRequest->len) <= static_cast<uint64_t>(maxOffset));
 158
 159     Mmapping mapping(fd, aRequest->len, PROT_READ, MAP_PRIVATE | MAP_NORESERVE,
 160                      aRequest->offset);
 161
 162     bool done = false;
 163     if (void *buf = mapping.map()) {
 164         memcpy(aRequest->buf, buf, aRequest->len);
 165         done = mapping.unmap();
 166     }
 167     error_ = !done;
 168
 169     const ssize_t rlen = error_ ? -1 : (ssize_t)aRequest->len;
 170     const int errflag = error_ ? DISK_ERROR :DISK_OK;
 171     ioRequestor->readCompleted(aRequest->buf, rlen, errflag, aRequest);
 172 }
 173
 174 void
 175 MmappedFile::write(WriteRequest *aRequest)
 176 {
 177     debugs(79,3, HERE << "(FD " << fd << ", " << aRequest->len << ", " <<
 178            aRequest->offset << ")");
 179
 180     assert(fd >= 0);
 181     assert(ioRequestor != NULL);
 182     assert(aRequest->len > 0); // TODO: work around mmap failures on zero-len?
 183     assert(aRequest->offset >= 0);
 184     assert(!error_); // TODO: propagate instead?
 185
 186     assert(minOffset < 0 || minOffset <= aRequest->offset);
 187     assert(maxOffset < 0 || static_cast<uint64_t>(aRequest->offset + aRequest->len) <= static_cast<uint64_t>(maxOffset));
 188
 189     const ssize_t written =
 190         pwrite(fd, aRequest->buf, aRequest->len, aRequest->offset);
 191     if (written < 0) {
 192         debugs(79, DBG_IMPORTANT, HERE << "error: " << xstrerr(errno));
 193         error_ = true;
 194     } else if (static_cast<size_t>(written) != aRequest->len) {
 195         debugs(79, DBG_IMPORTANT, HERE << "problem: " << written << " < " << aRequest->len);
 196         error_ = true;
 197     }
 198
 199     if (aRequest->free_func)
 200         (aRequest->free_func)(const_cast<char*>(aRequest->buf)); // broken API?
 201
 202     if (!error_) {
 203         debugs(79,5, HERE << "wrote " << aRequest->len << " to FD " << fd << " at " << aRequest->offset);
 204     } else {
 205         doClose();
 206     }
 207
 208     const ssize_t rlen = error_ ? 0 : (ssize_t)aRequest->len;
 209     const int errflag = error_ ? DISK_ERROR :DISK_OK;
 210     ioRequestor->writeCompleted(errflag, rlen, aRequest);
 211 }
 212
 213 /// we only support blocking I/O
 214 bool
 215 MmappedFile::ioInProgress() const
 216 {
 217     return false;
 218 }
 219
 220 Mmapping::Mmapping(int aFd, size_t aLength, int aProt, int aFlags, off_t anOffset):
 221     fd(aFd), length(aLength), prot(aProt), flags(aFlags), offset(anOffset),
 222     delta(-1), buf(NULL)
 223 {
 224 }
 225
 226 Mmapping::~Mmapping()
 227 {
 228     if (buf)
 229         unmap();
 230 }
 231
 232 void *
 233 Mmapping::map()
 234 {
 235     // mmap(2) requires that offset is a multiple of the page size
 236     static const int pageSize = getpagesize();
 237     delta = offset % pageSize;
 238
 239     buf = mmap(NULL, length + delta, prot, flags, fd, offset - delta);
 240
 241     if (buf == MAP_FAILED) {
 242         const int errNo = errno;
 243         debugs(79,3, HERE << "error FD " << fd << "mmap(" << length << '+' <<
 244                delta << ", " << offset << '-' << delta << "): " << xstrerr(errNo));
 245         buf = NULL;
 246         return NULL;
 247     }
 248
 249     return static_cast<char*>(buf) + delta;
 250 }
 251
 252 bool
 253 Mmapping::unmap()
 254 {
 255     debugs(79,9, HERE << "FD " << fd <<
 256            " munmap(" << buf << ", " << length << '+' << delta << ')');
 257
 258     if (!buf) // forgot or failed to map
 259         return false;
 260
 261     const bool error = munmap(buf, length + delta) != 0;
 262     if (error) {
 263         const int errNo = errno;
 264         debugs(79,3, HERE << "error FD " << fd <<
 265                " munmap(" << buf << ", " << length << '+' << delta << "): " <<
 266                "): " << xstrerr(errNo));
 267     }
 268     buf = NULL;
 269     return !error;
 270 }
 271
 272 // TODO: check MAP_NORESERVE, consider MAP_POPULATE and MAP_FIXED
 273