lib/savewd.h

   1 /* Save and restore the working directory, possibly using a subprocess.
   2
   3    Copyright (C) 2006, 2009-2020 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  20 #ifndef SAVEWD_H
  21 # define SAVEWD_H 1
  22
  23 #include <stdbool.h>
  24 #include <sys/types.h>
  25
  26 #ifndef _GL_INLINE_HEADER_BEGIN
  27  #error "Please include config.h first."
  28 #endif
  29 _GL_INLINE_HEADER_BEGIN
  30 #ifndef SAVEWD_INLINE
  31 # define SAVEWD_INLINE _GL_INLINE
  32 #endif
  33
  34 /* A saved working directory.  The member names and constants defined
  35    by this structure are private to the savewd module.  */
  36 struct savewd
  37 {
  38   /* The state of this object.  */
  39   enum
  40     {
  41       /* This object has been created but does not yet represent
  42          the working directory.  */
  43       INITIAL_STATE,
  44
  45       /* val.fd is the original working directory's file descriptor.
  46          It is still the working directory.  */
  47       FD_STATE,
  48
  49       /* Like FD_STATE, but the working directory has changed, so
  50          restoring it will require a fchdir.  */
  51       FD_POST_CHDIR_STATE,
  52
  53       /* Fork and let the subprocess do the work.  val.child is 0 in a
  54          child, negative in a childless parent, and the child process
  55          ID in a parent with a child.  */
  56       FORKING_STATE,
  57
  58       /* A serious problem argues against further efforts.  val.errnum
  59          contains the error number (e.g., EIO).  */
  60       ERROR_STATE,
  61
  62       /* savewd_finish has been called, so the application no longer
  63          cares whether the working directory is saved, and there is no
  64          more work to do.  */
  65       FINAL_STATE
  66     } state;
  67
  68   /* The object's value.  */
  69   union
  70   {
  71     int fd;
  72     int errnum;
  73     pid_t child;
  74   } val;
  75 };
  76
  77 /* Initialize a saved working directory object.  */
  78 SAVEWD_INLINE void
  79 savewd_init (struct savewd *wd)
  80 {
  81   wd->state = INITIAL_STATE;
  82 }
  83
  84
  85 /* Options for savewd_chdir.  Can be ORed together.  */
  86 enum
  87   {
  88     /* Do not follow symbolic links, if supported.  */
  89     SAVEWD_CHDIR_NOFOLLOW = 1,
  90
  91     /* Do not chdir if the directory is readable; simply succeed
  92        without invoking chdir if the directory was opened.  */
  93     SAVEWD_CHDIR_SKIP_READABLE = 2
  94   };
  95
  96 /* Change the directory, and if successful, record into *WD the fact
  97    that the process chdired into DIR.  A process using this module
  98    should use savewd_chdir rather than chdir or fchdir.  Obey the
  99    options specified in OPTIONS.
 100
 101    If OPEN_RESULT is not null, store into OPEN_RESULT[0] a file
 102    descriptor that accesses DIR if a file descriptor is successfully
 103    obtained.  Store -1 otherwise, setting OPEN_RESULT[1] to the error
 104    number.  Store through OPEN_RESULT regardless of whether the chdir
 105    is successful.  However, when -2 is returned, the contents of
 106    OPEN_RESULT are indeterminate since the file descriptor is closed
 107    in the parent.
 108
 109    Return -2 if a subprocess was spun off to do the real work, -1
 110    (setting errno) if unsuccessful, 0 if successful.  */
 111 int savewd_chdir (struct savewd *wd, char const *dir, int options,
 112                   int open_result[2]);
 113
 114 /* Restore the working directory from *WD.  STATUS indicates the exit
 115    status corresponding to the work done since the last save; this is
 116    used when the caller is in a subprocess.  Return 0 if successful,
 117    -1 (setting errno) on our failure, a positive subprocess exit
 118    status if the working directory was restored in the parent but the
 119    subprocess failed.  */
 120 int savewd_restore (struct savewd *wd, int status);
 121
 122 /* Return WD's error number, or 0 if WD is not in an error state.  */
 123 SAVEWD_INLINE int _GL_ATTRIBUTE_PURE
 124 savewd_errno (struct savewd const *wd)
 125 {
 126   return (wd->state == ERROR_STATE ? wd->val.errnum : 0);
 127 }
 128
 129 /* Deallocate any resources associated with WD.  A program that chdirs
 130    should restore before finishing.  */
 131 void savewd_finish (struct savewd *wd);
 132
 133 /* Process N_FILES file names, FILE[0] through FILE[N_FILES - 1].
 134    For each file name F, call ACT (F, WD, OPTIONS); ACT should invoke
 135    savewd_chdir as needed, and should return an exit status.  WD
 136    represents the working directory; it may be in an error state when
 137    ACT is called.
 138
 139    Save and restore the working directory as needed by the file name
 140    vector; assume that ACT does not require access to any relative
 141    file names other than its first argument, and that it is OK if the
 142    working directory is changed when this function returns.  Some
 143    actions may be applied in a subprocess.
 144
 145    Return the maximum exit status that any call to ACT returned, or
 146    EXIT_SUCCESS (i.e., 0) if no calls were made.  */
 147 int savewd_process_files (int n_files, char **file,
 148                           int (*act) (char *, struct savewd *, void *),
 149                           void *options);
 150
 151 _GL_INLINE_HEADER_END
 152
 153 #endif