PostgreSQL Source Code  git master
file_utils.c
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1 /*-------------------------------------------------------------------------
2  *
3  * File-processing utility routines.
4  *
5  * Assorted utility functions to work on files.
6  *
7  *
8  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
9  * Portions Copyright (c) 1994, Regents of the University of California
10  *
11  * src/common/file_utils.c
12  *
13  *-------------------------------------------------------------------------
14  */
15 #include "postgres_fe.h"
16 
17 #include <dirent.h>
18 #include <fcntl.h>
19 #include <sys/stat.h>
20 #include <unistd.h>
21 
22 #include "common/file_utils.h"
23 #include "common/logging.h"
24 
25 
26 /* Define PG_FLUSH_DATA_WORKS if we have an implementation for pg_flush_data */
27 #if defined(HAVE_SYNC_FILE_RANGE)
28 #define PG_FLUSH_DATA_WORKS 1
29 #elif defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
30 #define PG_FLUSH_DATA_WORKS 1
31 #endif
32 
33 /*
34  * pg_xlog has been renamed to pg_wal in version 10.
35  */
36 #define MINIMUM_VERSION_FOR_PG_WAL 100000
37 
38 #ifdef PG_FLUSH_DATA_WORKS
39 static int pre_sync_fname(const char *fname, bool isdir);
40 #endif
41 static void walkdir(const char *path,
42  int (*action) (const char *fname, bool isdir),
43  bool process_symlinks);
44 
45 /*
46  * Issue fsync recursively on PGDATA and all its contents.
47  *
48  * We fsync regular files and directories wherever they are, but we follow
49  * symlinks only for pg_wal (or pg_xlog) and immediately under pg_tblspc.
50  * Other symlinks are presumed to point at files we're not responsible for
51  * fsyncing, and might not have privileges to write at all.
52  *
53  * serverVersion indicates the version of the server to be fsync'd.
54  *
55  * Errors are reported but not considered fatal.
56  */
57 void
58 fsync_pgdata(const char *pg_data,
59  int serverVersion)
60 {
61  bool xlog_is_symlink;
62  char pg_wal[MAXPGPATH];
63  char pg_tblspc[MAXPGPATH];
64 
65  /* handle renaming of pg_xlog to pg_wal in post-10 clusters */
66  snprintf(pg_wal, MAXPGPATH, "%s/%s", pg_data,
67  serverVersion < MINIMUM_VERSION_FOR_PG_WAL ? "pg_xlog" : "pg_wal");
68  snprintf(pg_tblspc, MAXPGPATH, "%s/pg_tblspc", pg_data);
69 
70  /*
71  * If pg_wal is a symlink, we'll need to recurse into it separately,
72  * because the first walkdir below will ignore it.
73  */
74  xlog_is_symlink = false;
75 
76 #ifndef WIN32
77  {
78  struct stat st;
79 
80  if (lstat(pg_wal, &st) < 0)
81  pg_log_error("could not stat file \"%s\": %m", pg_wal);
82  else if (S_ISLNK(st.st_mode))
83  xlog_is_symlink = true;
84  }
85 #else
86  if (pgwin32_is_junction(pg_wal))
87  xlog_is_symlink = true;
88 #endif
89 
90  /*
91  * If possible, hint to the kernel that we're soon going to fsync the data
92  * directory and its contents.
93  */
94 #ifdef PG_FLUSH_DATA_WORKS
95  walkdir(pg_data, pre_sync_fname, false);
96  if (xlog_is_symlink)
97  walkdir(pg_wal, pre_sync_fname, false);
98  walkdir(pg_tblspc, pre_sync_fname, true);
99 #endif
100 
101  /*
102  * Now we do the fsync()s in the same order.
103  *
104  * The main call ignores symlinks, so in addition to specially processing
105  * pg_wal if it's a symlink, pg_tblspc has to be visited separately with
106  * process_symlinks = true. Note that if there are any plain directories
107  * in pg_tblspc, they'll get fsync'd twice. That's not an expected case
108  * so we don't worry about optimizing it.
109  */
110  walkdir(pg_data, fsync_fname, false);
111  if (xlog_is_symlink)
112  walkdir(pg_wal, fsync_fname, false);
113  walkdir(pg_tblspc, fsync_fname, true);
114 }
115 
116 /*
117  * Issue fsync recursively on the given directory and all its contents.
118  *
119  * This is a convenient wrapper on top of walkdir().
120  */
121 void
122 fsync_dir_recurse(const char *dir)
123 {
124  /*
125  * If possible, hint to the kernel that we're soon going to fsync the data
126  * directory and its contents.
127  */
128 #ifdef PG_FLUSH_DATA_WORKS
129  walkdir(dir, pre_sync_fname, false);
130 #endif
131 
132  walkdir(dir, fsync_fname, false);
133 }
134 
135 /*
136  * walkdir: recursively walk a directory, applying the action to each
137  * regular file and directory (including the named directory itself).
138  *
139  * If process_symlinks is true, the action and recursion are also applied
140  * to regular files and directories that are pointed to by symlinks in the
141  * given directory; otherwise symlinks are ignored. Symlinks are always
142  * ignored in subdirectories, ie we intentionally don't pass down the
143  * process_symlinks flag to recursive calls.
144  *
145  * Errors are reported but not considered fatal.
146  *
147  * See also walkdir in fd.c, which is a backend version of this logic.
148  */
149 static void
150 walkdir(const char *path,
151  int (*action) (const char *fname, bool isdir),
152  bool process_symlinks)
153 {
154  DIR *dir;
155  struct dirent *de;
156 
157  dir = opendir(path);
158  if (dir == NULL)
159  {
160  pg_log_error("could not open directory \"%s\": %m", path);
161  return;
162  }
163 
164  while (errno = 0, (de = readdir(dir)) != NULL)
165  {
166  char subpath[MAXPGPATH * 2];
167  struct stat fst;
168  int sret;
169 
170  if (strcmp(de->d_name, ".") == 0 ||
171  strcmp(de->d_name, "..") == 0)
172  continue;
173 
174  snprintf(subpath, sizeof(subpath), "%s/%s", path, de->d_name);
175 
176  if (process_symlinks)
177  sret = stat(subpath, &fst);
178  else
179  sret = lstat(subpath, &fst);
180 
181  if (sret < 0)
182  {
183  pg_log_error("could not stat file \"%s\": %m", subpath);
184  continue;
185  }
186 
187  if (S_ISREG(fst.st_mode))
188  (*action) (subpath, false);
189  else if (S_ISDIR(fst.st_mode))
190  walkdir(subpath, action, false);
191  }
192 
193  if (errno)
194  pg_log_error("could not read directory \"%s\": %m", path);
195 
196  (void) closedir(dir);
197 
198  /*
199  * It's important to fsync the destination directory itself as individual
200  * file fsyncs don't guarantee that the directory entry for the file is
201  * synced. Recent versions of ext4 have made the window much wider but
202  * it's been an issue for ext3 and other filesystems in the past.
203  */
204  (*action) (path, true);
205 }
206 
207 /*
208  * Hint to the OS that it should get ready to fsync() this file.
209  *
210  * Ignores errors trying to open unreadable files, and reports other errors
211  * non-fatally.
212  */
213 #ifdef PG_FLUSH_DATA_WORKS
214 
215 static int
216 pre_sync_fname(const char *fname, bool isdir)
217 {
218  int fd;
219 
220  fd = open(fname, O_RDONLY | PG_BINARY, 0);
221 
222  if (fd < 0)
223  {
224  if (errno == EACCES || (isdir && errno == EISDIR))
225  return 0;
226  pg_log_error("could not open file \"%s\": %m", fname);
227  return -1;
228  }
229 
230  /*
231  * We do what pg_flush_data() would do in the backend: prefer to use
232  * sync_file_range, but fall back to posix_fadvise. We ignore errors
233  * because this is only a hint.
234  */
235 #if defined(HAVE_SYNC_FILE_RANGE)
236  (void) sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WRITE);
237 #elif defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
238  (void) posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED);
239 #else
240 #error PG_FLUSH_DATA_WORKS should not have been defined
241 #endif
242 
243  (void) close(fd);
244  return 0;
245 }
246 
247 #endif /* PG_FLUSH_DATA_WORKS */
248 
249 /*
250  * fsync_fname -- Try to fsync a file or directory
251  *
252  * Ignores errors trying to open unreadable files, or trying to fsync
253  * directories on systems where that isn't allowed/required. Reports
254  * other errors non-fatally.
255  */
256 int
257 fsync_fname(const char *fname, bool isdir)
258 {
259  int fd;
260  int flags;
261  int returncode;
262 
263  /*
264  * Some OSs require directories to be opened read-only whereas other
265  * systems don't allow us to fsync files opened read-only; so we need both
266  * cases here. Using O_RDWR will cause us to fail to fsync files that are
267  * not writable by our userid, but we assume that's OK.
268  */
269  flags = PG_BINARY;
270  if (!isdir)
271  flags |= O_RDWR;
272  else
273  flags |= O_RDONLY;
274 
275  /*
276  * Open the file, silently ignoring errors about unreadable files (or
277  * unsupported operations, e.g. opening a directory under Windows), and
278  * logging others.
279  */
280  fd = open(fname, flags, 0);
281  if (fd < 0)
282  {
283  if (errno == EACCES || (isdir && errno == EISDIR))
284  return 0;
285  pg_log_error("could not open file \"%s\": %m", fname);
286  return -1;
287  }
288 
289  returncode = fsync(fd);
290 
291  /*
292  * Some OSes don't allow us to fsync directories at all, so we can ignore
293  * those errors. Anything else needs to be reported.
294  */
295  if (returncode != 0 && !(isdir && (errno == EBADF || errno == EINVAL)))
296  {
297  pg_log_error("could not fsync file \"%s\": %m", fname);
298  (void) close(fd);
299  return -1;
300  }
301 
302  (void) close(fd);
303  return 0;
304 }
305 
306 /*
307  * fsync_parent_path -- fsync the parent path of a file or directory
308  *
309  * This is aimed at making file operations persistent on disk in case of
310  * an OS crash or power failure.
311  */
312 int
313 fsync_parent_path(const char *fname)
314 {
315  char parentpath[MAXPGPATH];
316 
317  strlcpy(parentpath, fname, MAXPGPATH);
318  get_parent_directory(parentpath);
319 
320  /*
321  * get_parent_directory() returns an empty string if the input argument is
322  * just a file name (see comments in path.c), so handle that as being the
323  * current directory.
324  */
325  if (strlen(parentpath) == 0)
326  strlcpy(parentpath, ".", MAXPGPATH);
327 
328  if (fsync_fname(parentpath, true) != 0)
329  return -1;
330 
331  return 0;
332 }
333 
334 /*
335  * durable_rename -- rename(2) wrapper, issuing fsyncs required for durability
336  *
337  * Wrapper around rename, similar to the backend version.
338  */
339 int
340 durable_rename(const char *oldfile, const char *newfile)
341 {
342  int fd;
343 
344  /*
345  * First fsync the old and target path (if it exists), to ensure that they
346  * are properly persistent on disk. Syncing the target file is not
347  * strictly necessary, but it makes it easier to reason about crashes;
348  * because it's then guaranteed that either source or target file exists
349  * after a crash.
350  */
351  if (fsync_fname(oldfile, false) != 0)
352  return -1;
353 
354  fd = open(newfile, PG_BINARY | O_RDWR, 0);
355  if (fd < 0)
356  {
357  if (errno != ENOENT)
358  {
359  pg_log_error("could not open file \"%s\": %m", newfile);
360  return -1;
361  }
362  }
363  else
364  {
365  if (fsync(fd) != 0)
366  {
367  pg_log_error("could not fsync file \"%s\": %m", newfile);
368  close(fd);
369  return -1;
370  }
371  close(fd);
372  }
373 
374  /* Time to do the real deal... */
375  if (rename(oldfile, newfile) != 0)
376  {
377  pg_log_error("could not rename file \"%s\" to \"%s\": %m",
378  oldfile, newfile);
379  return -1;
380  }
381 
382  /*
383  * To guarantee renaming the file is persistent, fsync the file with its
384  * new name, and its containing directory.
385  */
386  if (fsync_fname(newfile, false) != 0)
387  return -1;
388 
389  if (fsync_parent_path(newfile) != 0)
390  return -1;
391 
392  return 0;
393 }
int fsync_fname(const char *fname, bool isdir)
Definition: file_utils.c:257
#define MINIMUM_VERSION_FOR_PG_WAL
Definition: file_utils.c:36
int fsync_parent_path(const char *fname)
Definition: file_utils.c:313
#define pg_log_error(...)
Definition: logging.h:79
int durable_rename(const char *oldfile, const char *newfile)
Definition: file_utils.c:340
int closedir(DIR *)
Definition: dirent.c:113
static void walkdir(const char *path, int(*action)(const char *fname, bool isdir), bool process_symlinks)
Definition: file_utils.c:150
Definition: dirent.h:9
static int fd(const char *x, int i)
Definition: preproc-init.c:105
#define PG_BINARY
Definition: c.h:1191
void fsync_pgdata(const char *pg_data, int serverVersion)
Definition: file_utils.c:58
#define fsync(fd)
Definition: win32_port.h:63
Definition: dirent.c:25
void fsync_dir_recurse(const char *dir)
Definition: file_utils.c:122
#define MAXPGPATH
DIR * opendir(const char *)
Definition: dirent.c:33
void get_parent_directory(char *path)
Definition: path.c:854
static char * pg_data
Definition: initdb.c:123
#define S_ISREG(m)
Definition: win32_port.h:299
#define stat(a, b)
Definition: win32_port.h:255
size_t strlcpy(char *dst, const char *src, size_t siz)
Definition: strlcpy.c:45
struct dirent * readdir(DIR *)
Definition: dirent.c:77
#define S_ISDIR(m)
Definition: win32_port.h:296
#define lstat(path, sb)
Definition: win32_port.h:244
char d_name[MAX_PATH]
Definition: dirent.h:14
#define close(a)
Definition: win32.h:12
#define snprintf
Definition: port.h:192
Datum subpath(PG_FUNCTION_ARGS)
Definition: ltree_op.c:241
bool pgwin32_is_junction(const char *path)