my_symlink2.cc

/* Copyright (c) 2000, 2023, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   Without limiting anything contained in the foregoing, this file,
   which is part of C Driver for MySQL (Connector/C), is also subject to the
   Universal FOSS Exception, version 1.0, a copy of which can be found at
   http://oss.oracle.com/licenses/universal-foss-exception.

   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, version 2.0, 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 St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
  @file mysys/my_symlink2.cc
  Advanced symlink handling.
  This is used in MyISAM to let users symlinks tables to different disk.
  The main idea with these functions is to automatically create, delete and
  rename files and symlinks like they would be one unit.
*/

#include "my_config.h"

#include <errno.h>
#include <string.h>

#include "m_string.h"
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_io.h"
#include "my_sys.h"
#include "my_thread_local.h"
#include "mysys_err.h"

File my_create_with_symlink(const char *linkname, const char *filename,
                            int createflags, int access_flags, myf MyFlags) {
#ifdef _WIN32
  if (linkname) filename = linkname;
  if (!(MyFlags & MY_DELETE_OLD)) {
    if (!access(filename, F_OK)) {
      errno = EEXIST;
      set_my_errno(EEXIST);
      MyOsError(my_errno(), EE_CANTCREATEFILE, MYF(0), filename);
      return -1;
    }
  }
  return my_create(filename, createflags, access_flags, MyFlags);
#else
  File file;
  int tmp_errno;
  /* Test if we should create a link */
  int create_link;
  char abs_linkname[FN_REFLEN];
  DBUG_TRACE;
  DBUG_PRINT("enter",
             ("linkname: %s  filename: %s", linkname ? linkname : "(null)",
              filename ? filename : "(null)"));

  if (!my_enable_symlinks) {
    DBUG_PRINT("info", ("Symlinks disabled"));
    /* Create only the file, not the link and file */
    create_link = 0;
    if (linkname) filename = linkname;
  } else {
    if (linkname) my_realpath(abs_linkname, linkname, MYF(0));
    create_link = (linkname && strcmp(abs_linkname, filename));
  }

  if (!(MyFlags & MY_DELETE_OLD)) {
    if (!access(filename, F_OK)) {
      errno = EEXIST;
      set_my_errno(EEXIST);
      MyOsError(my_errno(), EE_CANTCREATEFILE, MYF(0), filename);
      return -1;
    }
    if (create_link && !access(linkname, F_OK)) {
      errno = EEXIST;
      set_my_errno(EEXIST);
      MyOsError(my_errno(), EE_CANTCREATEFILE, MYF(0), linkname);
      return -1;
    }
  }

  if ((file = my_create(filename, createflags, access_flags, MyFlags)) >= 0) {
    if (create_link) {
      /* Delete old link/file */
      if (MyFlags & MY_DELETE_OLD) my_delete(linkname, MYF(0));
      /* Create link */
      if (my_symlink(filename, linkname, MyFlags)) {
        /* Fail, remove everything we have done */
        tmp_errno = my_errno();
        my_close(file, MYF(0));
        my_delete(filename, MYF(0));
        file = -1;
        set_my_errno(tmp_errno);
      }
    }
  }
  return file;
#endif  // !_WIN32
}

/*
  If the file was a symlink, delete both symlink and the file which the
  symlink pointed to.
*/

int my_delete_with_symlink(const char *name, myf MyFlags) {
#ifdef _WIN32
  return my_delete(name, MyFlags);
#else
  char link_name[FN_REFLEN];
  int was_symlink =
      (my_enable_symlinks && !my_readlink(link_name, name, MYF(0)));
  int result;
  DBUG_TRACE;

  if (!(result = my_delete(name, MyFlags))) {
    if (was_symlink) result = my_delete(link_name, MyFlags);
  }
  return result;
#endif  // _WIN32
}

/*
  If the file is a normal file, just rename it.
  If the file is a symlink:
   - Create a new file with the name 'to' that points at
     symlink_dir/basename(to)
   - Rename the symlinked file to symlink_dir/basename(to)
   - Delete 'from'
   If something goes wrong, restore everything.
*/

int my_rename_with_symlink(const char *from, const char *to, myf MyFlags) {
#ifdef _WIN32
  return my_rename(from, to, MyFlags);
#else
  char link_name[FN_REFLEN], tmp_name[FN_REFLEN];
  int was_symlink =
      (my_enable_symlinks && !my_readlink(link_name, from, MYF(0)));
  int result = 0;
  int name_is_different;
  DBUG_TRACE;

  if (!was_symlink) return my_rename(from, to, MyFlags);

  /* Change filename that symlink pointed to */
  my_stpcpy(tmp_name, to);
  fn_same(tmp_name, link_name, 1); /* Copy dir */
  name_is_different = strcmp(link_name, tmp_name);
  if (name_is_different && !access(tmp_name, F_OK)) {
    set_my_errno(EEXIST);
    if (MyFlags & MY_WME) {
      MyOsError(my_errno(), EE_CANTCREATEFILE, MYF(0), tmp_name);
    }
    return 1;
  }

  /* Create new symlink */
  if (my_symlink(tmp_name, to, MyFlags)) return 1;

  /*
    Rename symlinked file if the base name didn't change.
    This can happen if you use this function where 'from' and 'to' has
    the same basename and different directories.
   */

  if (name_is_different && my_rename(link_name, tmp_name, MyFlags)) {
    int save_errno = my_errno();
    my_delete(to, MyFlags); /* Remove created symlink */
    set_my_errno(save_errno);
    return 1;
  }

  /* Remove original symlink */
  if (my_delete(from, MyFlags)) {
    int save_errno = my_errno();
    /* Remove created link */
    my_delete(to, MyFlags);
    /* Rename file back */
    if (strcmp(link_name, tmp_name))
      (void)my_rename(tmp_name, link_name, MyFlags);
    set_my_errno(save_errno);
    result = 1;
  }
  return result;
#endif /* !_WIN32 */
}