// Copyright 2012 Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
//   notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright
//   notice, this list of conditions and the following disclaimer in the
//   documentation and/or other materials provided with the distribution.
// * Neither the name of Google Inc. nor the names of its contributors
//   may be used to endorse or promote products derived from this software
//   without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "fs.h"

#if defined(HAVE_CONFIG_H)
#   include "config.h"
#endif

#if defined(HAVE_UNMOUNT)
#   include <sys/param.h>
#   include <sys/mount.h>
#endif
#include <sys/stat.h>
#include <sys/wait.h>

#include <assert.h>
#include <dirent.h>
#include <err.h>
#include <errno.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "defs.h"
#include "error.h"


/// Specifies if a real unmount(2) is available.
///
/// We use this as a constant instead of a macro so that we can compile both
/// versions of the unmount code unconditionally.  This is a way to prevent
/// compilation bugs going unnoticed for long.
static const bool have_unmount2 =
#if defined(HAVE_UNMOUNT)
   true;
#else
   false;
#endif


#if !defined(UMOUNT)
/// Fake replacement value to the path to umount(8).
#   define UMOUNT "do-not-use-this-value"
#else
#   if defined(HAVE_UNMOUNT)
#       error "umount(8) detected when unmount(2) is also available"
#   endif
#endif


#if !defined(HAVE_UNMOUNT)
/// Fake unmount(2) function for systems without it.
///
/// This is only provided to allow our code to compile in all platforms
/// regardless of whether they actually have an unmount(2) or not.
///
/// \param unused_path The mount point to be unmounted.
/// \param unused_flags The flags to the unmount(2) call.
///
/// \return -1 to indicate error, although this should never happen.
static int
unmount(const char* KYUA_DEFS_UNUSED_PARAM(path),
       const int KYUA_DEFS_UNUSED_PARAM(flags))
{
   assert(false);
   return -1;
}
#endif


/// Scans a directory and executes a callback on each entry.
///
/// \param directory The directory to scan.
/// \param callback The function to execute on each entry.
/// \param argument A cookie to pass to the callback function.
///
/// \return True if the directory scan and the calls to the callback function
/// are all successful; false otherwise.
///
/// \note Errors are logged to stderr and do not stop the algorithm.
static bool
try_iterate_directory(const char* directory,
                     bool (*callback)(const char*, const void*),
                     const void* argument)
{
   bool ok = true;

   DIR* dirp = opendir(directory);
   if (dirp == NULL) {
       warn("opendir(%s) failed", directory);
       ok &= false;
   } else {
       struct dirent* dp;
       while ((dp = readdir(dirp)) != NULL) {
           const char* name = dp->d_name;
           if (strcmp(name, ".") == 0 || strcmp(name, "..") == 0)
               continue;

           char* subdir;
           const kyua_error_t error = kyua_fs_concat(&subdir, directory, name,
                                                     NULL);
           if (kyua_error_is_set(error)) {
               kyua_error_free(error);
               warn("path concatenation failed");
               ok &= false;
           } else {
               ok &= callback(subdir, argument);
               free(subdir);
           }
       }
       closedir(dirp);
   }

   return ok;
}


/// Stats a file, without following links.
///
/// \param path The file to stat.
/// \param [out] sb Pointer to the stat structure in which to place the result.
///
/// \return The stat structure on success; none on failure.
///
/// \note Errors are logged to stderr.
static bool
try_stat(const char* path, struct stat* sb)
{
   if (lstat(path, sb) == -1) {
       warn("lstat(%s) failed", path);
       return false;
   } else
       return true;
}


/// Removes a directory.
///
/// \param path The directory to remove.
///
/// \return True on success; false otherwise.
///
/// \note Errors are logged to stderr.
static bool
try_rmdir(const char* path)
{
   if (rmdir(path) == -1) {
       warn("rmdir(%s) failed", path);
       return false;
   } else
       return true;
}


/// Removes a file.
///
/// \param path The file to remove.
///
/// \return True on success; false otherwise.
///
/// \note Errors are logged to stderr.
static bool
try_unlink(const char* path)
{
   if (unlink(path) == -1) {
       warn("unlink(%s) failed", path);
       return false;
   } else
       return true;
}


/// Unmounts a mount point.
///
/// \param path The location to unmount.
///
/// \return True on success; false otherwise.
///
/// \note Errors are logged to stderr.
static bool
try_unmount(const char* path)
{
   const kyua_error_t error = kyua_fs_unmount(path);
   if (kyua_error_is_set(error)) {
       kyua_error_warn(error, "Cannot unmount %s", path);
       kyua_error_free(error);
       return false;
   } else
       return true;
}


/// Attempts to weaken the permissions of a file.
///
/// \param path The file to unprotect.
///
/// \return True on success; false otherwise.
///
/// \note Errors are logged to stderr.
static bool
try_unprotect(const char* path)
{
   static const mode_t new_mode = 0700;

   if (chmod(path, new_mode) == -1) {
       warnx("chmod(%s, %04o) failed", path, new_mode);
       return false;
   } else
       return true;
}


/// Attempts to weaken the permissions of a symbolic link.
///
/// \param path The symbolic link to unprotect.
///
/// \return True on success; false otherwise.
///
/// \note Errors are logged to stderr.
static bool
try_unprotect_symlink(const char* path)
{
   static const mode_t new_mode = 0700;

#if HAVE_WORKING_LCHMOD
   if (lchmod(path, new_mode) == -1) {
       warnx("lchmod(%s, %04o) failed", path, new_mode);
       return false;
   } else
       return true;
#else
   warnx("lchmod(%s, %04o) failed; system call not implemented", path,
         new_mode);
   return false;
#endif
}


/// Traverses a hierarchy unmounting any mount points in it.
///
/// \param current_path The file or directory to traverse.
/// \param raw_parent_sb The stat structure of the enclosing directory.
///
/// \return True on success; false otherwise.
///
/// \note Errors are logged to stderr and do not stop the algorithm.
static bool
recursive_unmount(const char* current_path, const void* raw_parent_sb)
{
   const struct stat* parent_sb = raw_parent_sb;

   struct stat current_sb;
   bool ok = try_stat(current_path, &current_sb);
   if (ok) {
       if (S_ISDIR(current_sb.st_mode)) {
           assert(!S_ISLNK(current_sb.st_mode));
           ok &= try_iterate_directory(current_path, recursive_unmount,
                                       &current_sb);
       }

       if (current_sb.st_dev != parent_sb->st_dev)
           ok &= try_unmount(current_path);
   }

   return ok;
}


/// Traverses a hierarchy and removes all of its contents.
///
/// This honors mount points: when a mount point is encountered, it is traversed
/// in search for other mount points, but no files within any of these are
/// removed.
///
/// \param current_path The file or directory to traverse.
/// \param raw_parent_sb The stat structure of the enclosing directory.
///
/// \return True on success; false otherwise.
///
/// \note Errors are logged to stderr and do not stop the algorithm.
static bool
recursive_cleanup(const char* current_path, const void* raw_parent_sb)
{
   const struct stat* parent_sb = raw_parent_sb;

   struct stat current_sb;
   bool ok = try_stat(current_path, &current_sb);
   if (ok) {
       // Weakening the protections of a file is just a best-effort operation.
       // If this fails, we may still be able to do the file/directory removal
       // later on, so ignore any failures from try_unprotect().
       //
       // One particular case in which this fails is if try_unprotect() is run
       // on a symbolic link that points to a file for which the unprotect is
       // not possible, and lchmod(3) is not available.
       if (S_ISLNK(current_sb.st_mode))
           try_unprotect_symlink(current_path);
       else
           try_unprotect(current_path);

       if (current_sb.st_dev != parent_sb->st_dev) {
           ok &= recursive_unmount(current_path, parent_sb);
           if (ok)
               ok &= recursive_cleanup(current_path, parent_sb);
       } else {
           if (S_ISDIR(current_sb.st_mode)) {
               assert(!S_ISLNK(current_sb.st_mode));
               ok &= try_iterate_directory(current_path, recursive_cleanup,
                                           &current_sb);
               ok &= try_rmdir(current_path);
           } else {
               ok &= try_unlink(current_path);
           }
       }
   }

   return ok;
}


/// Unmounts a file system using unmount(2).
///
/// \pre unmount(2) must be available; i.e. have_unmount2 must be true.
///
/// \param mount_point The file system to unmount.
///
/// \return An error object.
static kyua_error_t
unmount_with_unmount2(const char* mount_point)
{
   assert(have_unmount2);

   if (unmount(mount_point, 0) == -1) {
       return kyua_libc_error_new(errno, "unmount(%s) failed",
                                  mount_point);
   }

   return kyua_error_ok();
}


/// Unmounts a file system using umount(8).
///
/// \pre umount(2) must not be available; i.e. have_unmount2 must be false.
///
/// \param mount_point The file system to unmount.
///
/// \return An error object.
static kyua_error_t
unmount_with_umount8(const char* mount_point)
{
   assert(!have_unmount2);

   const pid_t pid = fork();
   if (pid == -1) {
       return kyua_libc_error_new(errno, "fork() failed");
   } else if (pid == 0) {
       const int ret = execlp(UMOUNT, "umount", mount_point, NULL);
       assert(ret == -1);
       err(EXIT_FAILURE, "Failed to execute " UMOUNT);
   }

   kyua_error_t error = kyua_error_ok();
   int status;
   if (waitpid(pid, &status, 0) == -1) {
       error = kyua_libc_error_new(errno, "waitpid(%d) failed", pid);
   } else {
       if (WIFEXITED(status)) {
           if (WEXITSTATUS(status) == EXIT_SUCCESS)
               assert(!kyua_error_is_set(error));
           else {
               error = kyua_libc_error_new(EBUSY, "unmount(%s) failed",
                                           mount_point);
           }
       } else
           error = kyua_libc_error_new(EFAULT, "umount(8) crashed");
   }
   return error;
}


/// Recursively removes a directory.
///
/// \param root The directory or file to remove.  Cannot be a mount point.
///
/// \return An error object.
kyua_error_t
kyua_fs_cleanup(const char* root)
{
   struct stat current_sb;
   bool ok = try_stat(root, &current_sb);
   if (ok)
       ok &= recursive_cleanup(root, &current_sb);

   if (!ok) {
       warnx("Cleanup of '%s' failed", root);
       return kyua_libc_error_new(EPERM, "Cleanup of %s failed", root);
   } else
       return kyua_error_ok();
}


/// Concatenates a set of strings to form a path.
///
/// \param [out] output Pointer to a dynamically-allocated string that will hold
///     the resulting path, if all goes well.
/// \param first First component of the path to concatenate.
/// \param ... All other components to concatenate.
///
/// \return An error if there is not enough memory to fulfill the request; OK
/// otherwise.
kyua_error_t
kyua_fs_concat(char** const output, const char* first, ...)
{
   va_list ap;
   const char* component;

   va_start(ap, first);
   size_t length = strlen(first) + 1;
   while ((component = va_arg(ap, const char*)) != NULL) {
       length += 1 + strlen(component);
   }
   va_end(ap);

   *output = (char*)malloc(length);
   if (output == NULL)
       return kyua_oom_error_new();
   char* iterator = *output;

   int added_size;
   added_size = snprintf(iterator, length, "%s", first);
   iterator += added_size; length -= added_size;

   va_start(ap, first);
   while ((component = va_arg(ap, const char*)) != NULL) {
       added_size = snprintf(iterator, length, "/%s", component);
       iterator += added_size; length -= added_size;
   }
   va_end(ap);

   return kyua_error_ok();
}


/// Queries the path to the current directory.
///
/// \param [out] out_cwd Dynamically-allocated pointer to a string holding the
///     current path.  The caller must use free() to release it.
///
/// \return An error object.
kyua_error_t
kyua_fs_current_path(char** out_cwd)
{
   char* cwd;
#if defined(HAVE_GETCWD_DYN)
   cwd = getcwd(NULL, 0);
#else
   {
       const char* static_cwd = ::getcwd(NULL, MAXPATHLEN);
       const kyua_error_t error = kyua_fs_concat(&cwd, static_cwd, NULL);
       if (kyua_error_is_set(error))
           return error;
   }
#endif
   if (cwd == NULL) {
       return kyua_libc_error_new(errno, "getcwd() failed");
   } else {
       *out_cwd = cwd;
       return kyua_error_ok();
   }
}


/// Converts a path to absolute.
///
/// \param original The path to convert; may already be absolute.
/// \param [out] output Pointer to a dynamically-allocated string that will hold
///     the absolute path, if all goes well.
///
/// \return An error if there is not enough memory to fulfill the request; OK
/// otherwise.
kyua_error_t
kyua_fs_make_absolute(const char* original, char** const output)
{
   if (original[0] == '/') {
       *output = (char*)malloc(strlen(original) + 1);
       if (output == NULL)
           return kyua_oom_error_new();
       strcpy(*output, original);
       return kyua_error_ok();
   } else {
       char* current_path;
       kyua_error_t error;

       error = kyua_fs_current_path(&current_path);
       if (kyua_error_is_set(error))
           return error;

       error = kyua_fs_concat(output, current_path, original, NULL);
       free(current_path);
       return error;
   }
}


/// Unmounts a file system.
///
/// \param mount_point The file system to unmount.
///
/// \return An error object.
kyua_error_t
kyua_fs_unmount(const char* mount_point)
{
   kyua_error_t error;

   // FreeBSD's unmount(2) requires paths to be absolute.  To err on the side
   // of caution, let's make it absolute in all cases.
   char* abs_mount_point;
   error = kyua_fs_make_absolute(mount_point, &abs_mount_point);
   if (kyua_error_is_set(error))
       goto out;

   static const int unmount_retries = 3;
   static const int unmount_retry_delay_seconds = 1;

   int retries = unmount_retries;
retry:
   if (have_unmount2) {
       error = unmount_with_unmount2(abs_mount_point);
   } else {
       error = unmount_with_umount8(abs_mount_point);
   }
   if (kyua_error_is_set(error)) {
       assert(kyua_error_is_type(error, "libc"));
       if (kyua_libc_error_errno(error) == EBUSY && retries > 0) {
           kyua_error_warn(error, "%s busy; unmount retries left %d",
                           abs_mount_point, retries);
           kyua_error_free(error);
           retries--;
           sleep(unmount_retry_delay_seconds);
           goto retry;
       }
   }

out:
   free(abs_mount_point);
   return error;
}

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