xapian-core  1.4.21
io_utils.cc
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1 
4 /* Copyright (C) 2004,2006,2007,2008,2009,2011,2012,2014,2015,2016 Olly Betts
5  * Copyright (C) 2010 Richard Boulton
6  *
7  * This program is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License as published by
9  * the Free Software Foundation; either version 2 of the License, or
10  * (at your option) any later version.
11  *
12  * This program is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
18  * along with this program; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 #include <config.h>
23 
24 #include "io_utils.h"
25 #include "posixy_wrapper.h"
26 
27 #include "safeunistd.h"
28 
29 #include <cerrno>
30 #include <cstring>
31 #include <string>
32 
33 #include <xapian/error.h>
34 
35 #include "noreturn.h"
36 #include "omassert.h"
37 #include "str.h"
38 
39 // Trying to include the correct headers with the correct defines set to
40 // get pread() and pwrite() prototyped on every platform without breaking any
41 // other platform is a real can of worms. So instead we probe for what
42 // prototypes (if any) are required in configure and put them into
43 // PREAD_PROTOTYPE and PWRITE_PROTOTYPE.
44 #if defined HAVE_PREAD && defined PREAD_PROTOTYPE
45 PREAD_PROTOTYPE
46 #endif
47 #if defined HAVE_PWRITE && defined PWRITE_PROTOTYPE
48 PWRITE_PROTOTYPE
49 #endif
50 
51 bool
52 io_unlink(const std::string & filename)
53 {
54  if (posixy_unlink(filename.c_str()) == 0) {
55  return true;
56  }
57  if (errno != ENOENT) {
58  throw Xapian::DatabaseError(filename + ": delete failed", errno);
59  }
60  return false;
61 }
62 
63 // The smallest fd we want to use for a writable handle.
64 const int MIN_WRITE_FD = 3;
65 
66 int
67 io_open_block_wr(const char * fname, bool anew)
68 {
69  // Use auto because on AIX O_CLOEXEC may be a 64-bit integer constant.
70  auto flags = O_RDWR | O_BINARY | O_CLOEXEC;
71  if (anew) flags |= O_CREAT | O_TRUNC;
72  int fd = ::open(fname, flags, 0666);
73  if (fd >= MIN_WRITE_FD || fd < 0) return fd;
74 
75  // We want to avoid using fd < MIN_WRITE_FD, in case some other code in
76  // the same process tries to write to stdout or stderr, which would end up
77  // corrupting our database.
78  int badfd = fd;
79 #ifdef F_DUPFD_CLOEXEC
80  // dup to the first unused fd >= MIN_WRITE_FD.
81  fd = fcntl(badfd, F_DUPFD_CLOEXEC, MIN_WRITE_FD);
82  // F_DUPFD_CLOEXEC may not be supported.
83  if (fd < 0 && errno == EINVAL)
84 #endif
85 #ifdef F_DUPFD
86  {
87  fd = fcntl(badfd, F_DUPFD, MIN_WRITE_FD);
88 # ifdef FD_CLOEXEC
89  if (fd >= 0)
90  (void)fcntl(fd, F_SETFD, FD_CLOEXEC);
91 # endif
92  }
93  int save_errno = errno;
94  (void)close(badfd);
95  errno = save_errno;
96 #else
97  {
98  char toclose[MIN_WRITE_FD];
99  memset(toclose, 0, sizeof(toclose));
100  fd = badfd;
101  do {
102  toclose[fd] = 1;
103  fd = dup(fd);
104  } while (fd >= 0 && fd < MIN_WRITE_FD);
105  int save_errno = errno;
106  for (badfd = 0; badfd != MIN_WRITE_FD; ++badfd)
107  if (toclose[badfd])
108  close(badfd);
109  if (fd < 0) {
110  errno = save_errno;
111  } else {
112 # ifdef FD_CLOEXEC
113  (void)fcntl(fd, F_SETFD, FD_CLOEXEC);
114 # endif
115  }
116  }
117 #endif
118  Assert(fd >= MIN_WRITE_FD || fd < 0);
119  return fd;
120 }
121 
122 size_t
123 io_read(int fd, char * p, size_t n, size_t min)
124 {
125  size_t total = 0;
126  while (n) {
127  ssize_t c = read(fd, p, n);
128  if (c <= 0) {
129  if (c == 0) {
130  if (total >= min) break;
131  throw Xapian::DatabaseCorruptError("Couldn't read enough (EOF)");
132  }
133  if (errno == EINTR) continue;
134  throw Xapian::DatabaseError("Error reading from file", errno);
135  }
136  p += c;
137  total += c;
138  n -= c;
139  }
140  return total;
141 }
142 
144 void
145 io_write(int fd, const char * p, size_t n)
146 {
147  while (n) {
148  ssize_t c = write(fd, p, n);
149  if (c < 0) {
150  if (errno == EINTR) continue;
151  throw Xapian::DatabaseError("Error writing to file", errno);
152  }
153  p += c;
154  n -= c;
155  }
156 }
157 
158 XAPIAN_NORETURN(
159  static void throw_block_error(const char * s, off_t b, int e = 0));
160 static void
161 throw_block_error(const char * s, off_t b, int e)
162 {
163  std::string m = s;
164  m += str(b);
165  throw Xapian::DatabaseError(m, e);
166 }
167 
168 #ifdef HAVE_POSIX_FADVISE
169 bool
170 io_readahead_block(int fd, size_t n, off_t b, off_t o)
171 {
172  o += b * n;
173  // Assume that any failure is likely to also happen for another call with
174  // the same fd.
175  return posix_fadvise(fd, o, n, POSIX_FADV_WILLNEED) == 0;
176 }
177 #endif
178 
179 void
180 io_read_block(int fd, char * p, size_t n, off_t b, off_t o)
181 {
182  o += b * n;
183  // Prefer pread if available since it's typically implemented as a
184  // separate syscall, and that eliminates the overhead of an extra syscall
185  // per block read.
186 #ifdef HAVE_PREAD
187  while (true) {
188  ssize_t c = pread(fd, p, n, o);
189  // We should get a full read most of the time, so streamline that case.
190  if (usual(c == ssize_t(n)))
191  return;
192  // -1 is error, 0 is EOF
193  if (c <= 0) {
194  if (c == 0)
195  throw_block_error("EOF reading block ", b);
196  // We get EINTR if the syscall was interrupted by a signal.
197  // In this case we should retry the read.
198  if (errno == EINTR) continue;
199  throw_block_error("Error reading block ", b, errno);
200  }
201  p += c;
202  n -= c;
203  o += c;
204  }
205 #else
206  if (rare(lseek(fd, o, SEEK_SET) < 0))
207  throw_block_error("Error seeking to block ", b, errno);
208  while (true) {
209  ssize_t c = read(fd, p, n);
210  // We should get a full read most of the time, so streamline that case.
211  if (usual(c == ssize_t(n)))
212  return;
213  if (c <= 0) {
214  if (c == 0)
215  throw_block_error("EOF reading block ", b);
216  // We get EINTR if the syscall was interrupted by a signal.
217  // In this case we should retry the read.
218  if (errno == EINTR) continue;
219  throw_block_error("Error reading block ", b, errno);
220  }
221  p += c;
222  n -= c;
223  }
224 #endif
225 }
226 
227 void
228 io_write_block(int fd, const char * p, size_t n, off_t b, off_t o)
229 {
230  o += b * n;
231  // Prefer pwrite if available since it's typically implemented as a
232  // separate syscall, and that eliminates the overhead of an extra syscall
233  // per block write.
234 #ifdef HAVE_PWRITE
235  while (true) {
236  ssize_t c = pwrite(fd, p, n, o);
237  // We should get a full write most of the time, so streamline that case.
238  if (usual(c == ssize_t(n)))
239  return;
240  if (c < 0) {
241  // We get EINTR if the syscall was interrupted by a signal.
242  // In this case we should retry the write.
243  if (errno == EINTR) continue;
244  throw_block_error("Error writing block ", b, errno);
245  }
246  p += c;
247  n -= c;
248  o += c;
249  }
250 #else
251  if (rare(lseek(fd, o, SEEK_SET) < 0))
252  throw_block_error("Error seeking to block ", b, errno);
253  while (true) {
254  ssize_t c = write(fd, p, n);
255  // We should get a full write most of the time, so streamline that case.
256  if (usual(c == ssize_t(n)))
257  return;
258  if (c < 0) {
259  // We get EINTR if the syscall was interrupted by a signal.
260  // In this case we should retry the write.
261  if (errno == EINTR) continue;
262  throw_block_error("Error writing block ", b, errno);
263  }
264  p += c;
265  n -= c;
266  }
267 #endif
268 }
269 
270 bool
271 io_tmp_rename(const std::string & tmp_file, const std::string & real_file)
272 {
273 #ifdef EXDEV
274  // We retry on EXDEV a few times as some older Linux kernels are buggy and
275  // fail with EXDEV when the two files are on the same device (as they
276  // always ought to be when this function is used). Don't retry forever in
277  // case someone calls this with files on different devices.
278  //
279  // We're not sure exactly which kernels are buggy in this way, but there's
280  // discussion here: https://www.spinics.net/lists/linux-nfs/msg17306.html
281  //
282  // Reported at: https://trac.xapian.org/ticket/698
283  int retries = 5;
284 retry:
285 #endif
286  if (posixy_rename(tmp_file.c_str(), real_file.c_str()) < 0) {
287 #ifdef EXDEV
288  if (errno == EXDEV && --retries > 0) goto retry;
289 #endif
290  // With NFS, rename() failing may just mean that the server crashed
291  // after successfully renaming, but before reporting this, and then
292  // the retried operation fails. So we need to check if the source
293  // file still exists, which we do by calling unlink(), since we want
294  // to remove the temporary file anyway.
295  int saved_errno = errno;
296  if (unlink(tmp_file.c_str()) == 0 || errno != ENOENT) {
297  errno = saved_errno;
298  return false;
299  }
300  }
301  return true;
302 }
int close(FD &fd)
Definition: fd.h:63
#define Assert(COND)
Definition: omassert.h:122
Define the XAPIAN_NORETURN macro.
void io_write(int fd, const char *p, size_t n)
Write n bytes from block pointed to by p to file descriptor fd.
Definition: io_utils.cc:145
bool io_unlink(const std::string &filename)
Delete a file.
Definition: io_utils.cc:52
void io_read_block(int fd, char *p, size_t n, off_t b, off_t o)
Read block b size n bytes into buffer p from file descriptor fd, offset o.
Definition: io_utils.cc:180
#define usual(COND)
Definition: config.h:574
Provides wrappers with POSIXy semantics.
#define posixy_rename(F, T)
int io_open_block_wr(const char *fname, bool anew)
Open a block-based file for writing.
Definition: io_utils.cc:67
#define O_BINARY
Definition: safefcntl.h:81
WritableDatabase open()
Construct a WritableDatabase object for a new, empty InMemory database.
Definition: dbfactory.h:104
bool io_readahead_block(int, size_t, off_t, off_t=0)
Readahead block b size n bytes from file descriptor fd.
Definition: io_utils.h:133
Convert types to std::string.
#define O_CLOEXEC
Definition: safefcntl.h:90
#define rare(COND)
Definition: config.h:573
static void throw_block_error(const char *s, off_t b, int e=0)
Definition: io_utils.cc:161
Hierarchy of classes which Xapian can throw as exceptions.
#define posixy_unlink(F)
void io_write_block(int fd, const char *p, size_t n, off_t b, off_t o)
Write block b size n bytes from buffer p to file descriptor fd, offset o.
Definition: io_utils.cc:228
string str(int value)
Convert int to std::string.
Definition: str.cc:90
bool io_tmp_rename(const std::string &tmp_file, const std::string &real_file)
Rename a temporary file to its final position.
Definition: io_utils.cc:271
const int MIN_WRITE_FD
Definition: io_utils.cc:64
size_t io_read(int fd, char *p, size_t n, size_t min)
Read n bytes (or until EOF) into block pointed to by p from file descriptor fd.
Definition: io_utils.cc:123
DatabaseCorruptError indicates database corruption was detected.
Definition: error.h:409
Wrappers for low-level POSIX I/O routines.
<unistd.h>, but with compat.
Various assertion macros.
DatabaseError indicates some sort of database related error.
Definition: error.h:367