--- /dev/null
+/* Save and restore the working directory, possibly using a child process.
+
+ Copyright (C) 2006 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2, or (at your option)
+ any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software Foundation,
+ Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+
+/* Written by Paul Eggert. */
+
+#include <config.h>
+
+#include "savewd.h"
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "exit.h"
+#include "dirname.h"
+#include "fcntl-safer.h"
+
+
+/* Save the working directory into *WD, if it hasn't been saved
+ already. Return true if a child has been forked to do the real
+ work. */
+static bool
+savewd_save (struct savewd *wd)
+{
+ switch (wd->state)
+ {
+ case INITIAL_STATE:
+ /* Save the working directory, or prepare to fall back if possible. */
+ {
+ int fd = open_safer (".", O_RDONLY);
+ if (0 <= fd)
+ {
+ wd->state = FD_STATE;
+ wd->val.fd = fd;
+ break;
+ }
+ if (errno != EACCES)
+ {
+ wd->state = ERROR_STATE;
+ wd->val.errnum = errno;
+ break;
+ }
+ }
+ wd->state = FORKING_STATE;
+ wd->val.child = -1;
+ /* Fall through. */
+ case FORKING_STATE:
+ if (wd->val.child < 0)
+ {
+ /* "Save" the initial working directory by forking a new
+ subprocess that will attempt all the work from the chdir
+ until until the next savewd_restore. */
+ wd->val.child = fork ();
+ if (wd->val.child != 0)
+ {
+ if (0 < wd->val.child)
+ return true;
+ wd->state = ERROR_STATE;
+ wd->val.errnum = errno;
+ }
+ }
+ break;
+
+ case FD_STATE:
+ case FD_POST_CHDIR_STATE:
+ case ERROR_STATE:
+ case FINAL_STATE:
+ break;
+
+ default:
+ assert (false);
+ }
+
+ return false;
+}
+
+int
+savewd_chdir (struct savewd *wd, char const *dir, int options,
+ int open_result[2])
+{
+ int fd = -1;
+ int result = 0;
+
+ /* Open the directory if requested, or if avoiding a race condition
+ is requested and possible. */
+ if (open_result || (options & (O_NOFOLLOW ? SAVEWD_CHDIR_NOFOLLOW : 0)))
+ {
+ fd = open (dir,
+ (O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK
+ | (options & SAVEWD_CHDIR_NOFOLLOW ? O_NOFOLLOW : 0)));
+
+ if (open_result)
+ {
+ open_result[0] = fd;
+ open_result[1] = errno;
+ }
+
+ if (fd < 0 && (errno != EACCES || (options & SAVEWD_CHDIR_READABLE)))
+ result = -1;
+ }
+
+ if (result == 0 && ! (0 <= fd && options & SAVEWD_CHDIR_SKIP_READABLE))
+ {
+ if (savewd_save (wd))
+ {
+ open_result = NULL;
+ result = -2;
+ }
+ else
+ {
+ result = (fd < 0 ? chdir (dir) : fchdir (fd));
+
+ if (result == 0)
+ switch (wd->state)
+ {
+ case FD_STATE:
+ wd->state = FD_POST_CHDIR_STATE;
+ break;
+
+ case ERROR_STATE:
+ case FD_POST_CHDIR_STATE:
+ case FINAL_STATE:
+ break;
+
+ case FORKING_STATE:
+ assert (wd->val.child == 0);
+ break;
+
+ default:
+ assert (false);
+ }
+ }
+ }
+
+ if (0 <= fd && ! open_result)
+ {
+ int e = errno;
+ close (fd);
+ errno = e;
+ }
+
+ return result;
+}
+
+int
+savewd_restore (struct savewd *wd, int status)
+{
+ switch (wd->state)
+ {
+ case INITIAL_STATE:
+ case FD_STATE:
+ /* The working directory is the desired directory, so there's no
+ work to do. */
+ break;
+
+ case FD_POST_CHDIR_STATE:
+ /* Restore the working directory using fchdir. */
+ if (fchdir (wd->val.fd) == 0)
+ {
+ wd->state = FD_STATE;
+ break;
+ }
+ else
+ {
+ int chdir_errno = errno;
+ close (wd->val.fd);
+ wd->state = ERROR_STATE;
+ wd->val.errnum = chdir_errno;
+ }
+ /* Fall through. */
+ case ERROR_STATE:
+ /* Report an error if asked to restore the working directory. */
+ errno = wd->val.errnum;
+ return -1;
+
+ case FORKING_STATE:
+ /* "Restore" the working directory by waiting for the subprocess
+ to finish. */
+ {
+ pid_t child = wd->val.child;
+ if (child == 0)
+ _exit (status);
+ if (0 < child)
+ {
+ int status;
+ while (waitpid (child, &status, 0) < 0)
+ assert (errno == EINTR);
+ wd->val.child = -1;
+ if (! WIFEXITED (status))
+ raise (WTERMSIG (status));
+ return WEXITSTATUS (status);
+ }
+ }
+ break;
+
+ default:
+ assert (false);
+ }
+
+ return 0;
+}
+
+void
+savewd_finish (struct savewd *wd)
+{
+ switch (wd->state)
+ {
+ case INITIAL_STATE:
+ case ERROR_STATE:
+ break;
+
+ case FD_STATE:
+ case FD_POST_CHDIR_STATE:
+ close (wd->val.fd);
+ break;
+
+ case FORKING_STATE:
+ assert (wd->val.child < 0);
+ break;
+
+ default:
+ assert (false);
+ }
+
+ wd->state = FINAL_STATE;
+}
+
+/* Return true if the actual work is currently being done by a
+ subprocess.
+
+ A true return means that the caller and the subprocess should
+ resynchronize later with savewd_restore, using only their own
+ memory to decide when to resynchronize; they should not consult the
+ file system to decide, because that might lead to race conditions.
+ This is why savewd_chdir is broken out into another function;
+ savewd_chdir's callers _can_ inspect the file system to decide
+ whether to call savewd_chdir. */
+static inline bool
+savewd_delegating (struct savewd const *wd)
+{
+ return wd->state == FORKING_STATE && 0 < wd->val.child;
+}
+
+int
+savewd_process_files (int n_files, char **file,
+ int (*act) (char *, struct savewd *, void *),
+ void *options)
+{
+ int i = 0;
+ int last_relative;
+ int exit_status = EXIT_SUCCESS;
+ struct savewd wd;
+ savewd_init (&wd);
+
+ for (last_relative = n_files - 1; 0 <= last_relative; last_relative--)
+ if (! IS_ABSOLUTE_FILE_NAME (file[last_relative]))
+ break;
+
+ for (; i < last_relative; i++)
+ {
+ if (! savewd_delegating (&wd))
+ {
+ int s = act (file[i], &wd, options);
+ if (exit_status < s)
+ exit_status = s;
+ }
+
+ if (! IS_ABSOLUTE_FILE_NAME (file[i + 1]))
+ {
+ int r = savewd_restore (&wd, exit_status);
+ if (exit_status < r)
+ exit_status = r;
+ }
+ }
+
+ savewd_finish (&wd);
+
+ for (; i < n_files; i++)
+ {
+ int s = act (file[i], &wd, options);
+ if (exit_status < s)
+ exit_status = s;
+ }
+
+ return exit_status;
+}
--- /dev/null
+/* Save and restore the working directory, possibly using a subprocess.
+
+ Copyright (C) 2006 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2, or (at your option)
+ any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software Foundation,
+ Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+
+/* Written by Paul Eggert. */
+
+#ifndef SAVEWD_H
+# define SAVEWD_H 1
+
+#include <stdbool.h>
+#include <sys/types.h>
+
+/* A saved working directory. The member names and constants defined
+ by this structure are private to the savewd module. */
+struct savewd
+{
+ /* The state of this object. */
+ enum
+ {
+ /* This object has been created but does not yet represent
+ the working directory. */
+ INITIAL_STATE,
+
+ /* val.fd is the original working directory's file descriptor.
+ It is still the working directory. */
+ FD_STATE,
+
+ /* Like FD_STATE, but the working directory has changed, so
+ restoring it will require a fchdir. */
+ FD_POST_CHDIR_STATE,
+
+ /* Fork and let the subprocess do the work. val.child is 0 in a
+ child, negative in a childless parent, and the child process
+ ID in a parent with a child. */
+ FORKING_STATE,
+
+ /* A serious problem argues against further efforts. val.errnum
+ contains the error number (e.g., EIO). */
+ ERROR_STATE,
+
+ /* savewd_finish has been called, so the application no longer
+ cares whether the working directory is saved, and there is no
+ more work to do. */
+ FINAL_STATE
+ } state;
+
+ /* The object's value. */
+ union
+ {
+ int fd;
+ int errnum;
+ pid_t child;
+ } val;
+};
+
+/* Initialize a saved working directory object. */
+static inline void
+savewd_init (struct savewd *wd)
+{
+ wd->state = INITIAL_STATE;
+}
+
+
+/* Options for savewd_chdir. */
+enum
+ {
+ /* Do not follow symbolic links, if supported. */
+ SAVEWD_CHDIR_NOFOLLOW = 1,
+
+ /* The directory should be readable, so fail if it happens to be
+ discovered that the directory is not readable. (Unreadable
+ directories are not necessarily diagnosed, though.) */
+ SAVEWD_CHDIR_READABLE = 2,
+
+ /* Do not chdir if the directory is readable; simply succeed
+ without invoking chdir if the directory was opened. */
+ SAVEWD_CHDIR_SKIP_READABLE = 4
+ };
+
+/* Change the directory, and if successful, record into *WD the fact
+ that the process chdired into DIR. A process using this module
+ should use savewd_chdir rather than chdir or fchdir. Obey the
+ options specified in OPTIONS.
+
+ If OPEN_RESULT is not null, store into OPEN_RESULT[0] a file
+ descriptor that accesses DIR if a file descriptor is successfully
+ obtained. Store -1 otherwise, setting OPEN_RESULT[1] to the error
+ number. Store through OPEN_RESULT regardless of whether the chdir
+ is successful. However, when -2 is returned, the contents of
+ OPEN_RESULT are indeterminate since the file descriptor is closed
+ in the parent.
+
+ Return -2 if a subprocess was spun off to do the real work, -1
+ (setting errno) if unsuccessful, 0 if successful. */
+int savewd_chdir (struct savewd *wd, char const *dir, int options,
+ int open_result[2]);
+
+/* Restore the working directory from *WD. STATUS indicates the exit
+ status corresponding to the work done since the last save; this is
+ used when the caller is in a subprocess. Return 0 if successful,
+ -1 (setting errno) on our failure, a positive subprocess exit
+ status if the working directory was restored in the parent but the
+ subprocess failed. */
+int savewd_restore (struct savewd *wd, int status);
+
+/* Return WD's error number, or 0 if WD is not in an error state. */
+static inline int
+savewd_errno (struct savewd const *wd)
+{
+ return (wd->state == ERROR_STATE ? wd->val.errnum : 0);
+}
+
+/* Deallocate any resources associated with WD. A program that chdirs
+ should restore before finishing. */
+void savewd_finish (struct savewd *wd);
+
+/* Process N_FILES file names, FILE[0] through FILE[N_FILES - 1].
+ For each file name F, call ACT (F, WD, OPTIONS); ACT should invoke
+ savewd_chdir as needed, and should return an exit status. WD
+ represents thw working directory; it may be in an error state when
+ ACT is called.
+
+ Save and restore the working directory as needed by the file name
+ vector; assume that ACT does not require access to any relative
+ file names other than its first argument, and that it is OK if the
+ working directory is changed when this function returns. Some
+ actions may be applied in a subprocess.
+
+ Return the maximum exit status that any call to ACT returned, or
+ EXIT_SUCCESS (i.e., 0) if no calls were made. */
+int savewd_process_files (int n_files, char **file,
+ int (*act) (char *, struct savewd *, void *),
+ void *options);
+
+#endif
--- /dev/null
+# Save and restore the working directory, possibly using a child process.
+
+dnl Copyright (C) 2004 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_SAVEWD],
+ [AC_REQUIRE([AC_C_INLINE])])
--- /dev/null
+Description:
+Save and restore the working directory, possibly using a child process.
+
+Files:
+lib/savewd.h
+lib/savewd.c
+m4/savewd.m4
+
+Depends-on:
+dirname
+exit
+fcntl-safer
+stdbool
+xalloc
+
+configure.ac:
+gl_SAVEWD
+
+Makefile.am:
+lib_SOURCES += savewd.h savewd.c
+
+Include:
+"savewd.h"
+
+License:
+GPL
+
+Maintainer:
+Paul Eggert, Jim Meyering
projects / gnulib.git / commitdiff