lib/savewd.h

   1 /* Save and restore the working directory, possibly using a subprocess.
   2
   3    Copyright (C) 2006, 2009-2024 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 /* This file uses _GL_INLINE_HEADER_BEGIN, _GL_INLINE, _GL_ATTRIBUTE_PURE.  */
  24 #if !_GL_CONFIG_H_INCLUDED
  25  #error "Please include config.h first."
  26 #endif
  27
  28 #include <sys/types.h>
  29
  30 _GL_INLINE_HEADER_BEGIN
  31 #ifndef SAVEWD_INLINE
  32 # define SAVEWD_INLINE _GL_INLINE
  33 #endif
  34
  35 /* A saved working directory.  The member names and constants defined
  36    by this structure are private to the savewd module.  */
  37 struct savewd
  38 {
  39   /* The state of this object.  */
  40   enum
  41     {
  42       /* This object has been created but does not yet represent
  43          the working directory.  */
  44       INITIAL_STATE,
  45
  46       /* val.fd is the original working directory's file descriptor.
  47          It is still the working directory.  */
  48       FD_STATE,
  49
  50       /* Like FD_STATE, but the working directory has changed, so
  51          restoring it will require a fchdir.  */
  52       FD_POST_CHDIR_STATE,
  53
  54       /* Fork and let the subprocess do the work.  val.child is 0 in a
  55          child, negative in a childless parent, and the child process
  56          ID in a parent with a child.  */
  57       FORKING_STATE,
  58
  59       /* A serious problem argues against further efforts.  val.errnum
  60          contains the error number (e.g., EIO).  */
  61       ERROR_STATE,
  62
  63       /* savewd_finish has been called, so the application no longer
  64          cares whether the working directory is saved, and there is no
  65          more work to do.  */
  66       FINAL_STATE
  67     } state;
  68
  69   /* The object's value.  */
  70   union
  71   {
  72     int fd;
  73     int errnum;
  74     pid_t child;
  75   } val;
  76 };
  77
  78 /* Initialize a saved working directory object.  */
  79 SAVEWD_INLINE void
  80 savewd_init (struct savewd *wd)
  81 {
  82   wd->state = INITIAL_STATE;
  83 }
  84
  85
  86 /* Options for savewd_chdir.  Can be ORed together.  */
  87 enum
  88   {
  89     /* Do not follow symbolic links, if supported.  */
  90     SAVEWD_CHDIR_NOFOLLOW = 1,
  91
  92     /* Do not chdir if the directory is readable; simply succeed
  93        without invoking chdir if the directory was opened.  */
  94     SAVEWD_CHDIR_SKIP_READABLE = 2
  95   };
  96
  97 /* Change the directory, and if successful, record into *WD the fact
  98    that the process chdired into DIR.  A process using this module
  99    should use savewd_chdir rather than chdir or fchdir.  Obey the
 100    options specified in OPTIONS.
 101
 102    If OPEN_RESULT is not null, store into OPEN_RESULT[0] a file
 103    descriptor that accesses DIR if a file descriptor is successfully
 104    obtained.  Store -1 otherwise, setting OPEN_RESULT[1] to the error
 105    number.  Store through OPEN_RESULT regardless of whether the chdir
 106    is successful.  However, when -2 is returned, the contents of
 107    OPEN_RESULT are indeterminate since the file descriptor is closed
 108    in the parent.
 109
 110    Return -2 if a subprocess was spun off to do the real work, -1
 111    (setting errno) if unsuccessful, 0 if successful.  */
 112 int savewd_chdir (struct savewd *wd, char const *dir, int options,
 113                   int open_result[2]);
 114
 115 /* Restore the working directory from *WD.  STATUS indicates the exit
 116    status corresponding to the work done since the last save; this is
 117    used when the caller is in a subprocess.  Return 0 if successful,
 118    -1 (setting errno) on our failure, a positive subprocess exit
 119    status if the working directory was restored in the parent but the
 120    subprocess failed.  */
 121 int savewd_restore (struct savewd *wd, int status);
 122
 123 /* Return WD's error number, or 0 if WD is not in an error state.  */
 124 SAVEWD_INLINE int _GL_ATTRIBUTE_PURE
 125 savewd_errno (struct savewd const *wd)
 126 {
 127   return (wd->state == ERROR_STATE ? wd->val.errnum : 0);
 128 }
 129
 130 /* Deallocate any resources associated with WD.  A program that chdirs
 131    should restore before finishing.  */
 132 void savewd_finish (struct savewd *wd);
 133
 134 /* Process N_FILES file names, FILE[0] through FILE[N_FILES - 1].
 135    For each file name F, call ACT (F, WD, OPTIONS); ACT should invoke
 136    savewd_chdir as needed, and should return an exit status.  WD
 137    represents the working directory; it may be in an error state when
 138    ACT is called.
 139
 140    Save and restore the working directory as needed by the file name
 141    vector; assume that ACT does not require access to any relative
 142    file names other than its first argument, and that it is OK if the
 143    working directory is changed when this function returns.  Some
 144    actions may be applied in a subprocess.
 145
 146    Return the maximum exit status that any call to ACT returned, or
 147    EXIT_SUCCESS (i.e., 0) if no calls were made.  */
 148 int savewd_process_files (int n_files, char **file,
 149                           int (*act) (char *, struct savewd *, void *),
 150                           void *options);
 151
 152 _GL_INLINE_HEADER_END
 153
 154 #endif