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Re: New command to check NT's hibernation state


From: Peter Lustig
Subject: Re: New command to check NT's hibernation state
Date: Sat, 17 Dec 2011 22:16:50 -0500
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20111105 Thunderbird/8.0

On 17.12.2011 00:41, Vladimir 'phcoder' Serbinenko wrote:

/* nthibr.c - tests whether an MS Windows system partition is
hibernated */
/*
   *  GRUB  --  GRand Unified Bootloader
   *  Copyright (C) 2007,2008,2009,2011  Free Software Foundation, Inc.
   *
   *  GRUB 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 3 of the License, or
   *  (at your option) any later version.
   *
   *  GRUB 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 GRUB.  If not, see<http://www.gnu.org/licenses/>.
   */

#include<grub/types.h>
#include<grub/mm.h>
#include<grub/disk.h>
#include<grub/file.h>
#include<grub/misc.h>
#include<grub/dl.h>
#include<grub/extcmd.h>
#include<grub/lib/arg.h>
#include<grub/err.h>
#include<grub/i18n.h>

GRUB_MOD_LICENSE("GPLv3+");

/* Define this 'empty' array to let the '-h' and '-u' switches be
processed */
static const struct grub_arg_option options[] = {
    {0, 0, 0, 0, 0, 0}
};
Please remove this and use grub_command_t
I understand now.  What threw me off was seeing the 'hello' module use
'extcmd.'
static grub_err_t
grub_cmd_nthibr (grub_extcmd_context_t ctxt __attribute__ ((unused)),
                   int argc, char **args)
{
    char *partition_name = 0, *hibr_file_path = 0, hibr_file_magic[5];
    grub_size_t name_length;
    grub_ssize_t magic_size;
    grub_disk_t partition;
    grub_file_t hibr_file = 0;

    /* Check argument count */
    if (!argc)
      return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("too few arguments"));
    else if (argc>   1)
      return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("too many
arguments"));

Either ignore trailing argument or put both in one check != 1
    /* Make copy of partition specifier, so it can be modified (if
needed) */
    name_length = grub_strlen (args[0]);
    partition_name = grub_zalloc (name_length + 3);
    if (!partition_name)
      goto exit;
    grub_strcpy (partition_name, args[0]);

    /* Ensure partition specifier start with a '(' */
    if (partition_name[0] != '(')
      {
        grub_memmove (partition_name + 1, partition_name, name_length++);
        partition_name[0] = '(';
      }

    /* Ensure partition specifier ends with a ')' */
    if (partition_name[name_length - 1] != ')')
      partition_name[(++name_length) - 1] = ')';

    /* Check if partition actually exists */
    partition_name[name_length - 1] = '\0';
    partition = grub_disk_open (partition_name + 1);
    if (!partition)
      goto exit;
    grub_disk_close (partition);
    partition_name[name_length - 1] = ')';

    /* Build path to 'hiberfil.sys' */
    hibr_file_path = grub_malloc ((grub_strlen (partition_name)
                                   + grub_strlen ("/hiberfil.sys") + 1));
    if (!hibr_file_path)
      goto exit;
    grub_strcpy (hibr_file_path, partition_name);
    grub_strcat (hibr_file_path, "/hiberfil.sys");

It would be more efficient if you just try to open file and see what
error you get. Actually you don't even need to distinguish between
error cases here since you return the error you encountered. This will
also save one useless alloc.
    /* Try to open 'hiberfil.sys' */
    hibr_file = grub_file_open (hibr_file_path);
    if (!hibr_file)
      {
        if (grub_errno == GRUB_ERR_FILE_NOT_FOUND)
          grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("'hiberfil.sys' not
found"));
This overriding is unnecessary. FS code already provides this message
This was intentional:  the default message ('file not found') is not
particularly helpful in this case since the
command's description nowhere mentions what file it's looking for (let
alone that any file is needed for it to
function).  I've updated this section to pop the first error off the
stack to eliminate the duplication (and added
a descriptive comment).
        goto exit;
      }

    /* Try to read magic number of 'hiberfil.sys' */
    magic_size = sizeof (hibr_file_magic) - 1;
    grub_memset (hibr_file_magic, 0, sizeof (hibr_file_magic));
    if (grub_file_read (hibr_file, hibr_file_magic, magic_size)<
magic_size)
      {
        if (!grub_errno)
          grub_error (GRUB_ERR_BAD_FILE_TYPE, N_("'hiberfil.sys' too
small"));
        goto exit;
      }

    /* Return SUCCESS if magic indicates file is active; else return
FAILURE */
    if (!grub_strncasecmp ("hibr", hibr_file_magic, magic_size))
      grub_error (GRUB_ERR_NONE, "true");
    else
      grub_error (GRUB_ERR_TEST_FAILURE, "false");

exit:
    /* Ensure unmanaged resources are cleaned up */
    if (partition_name)
      grub_free (partition_name);
    if (hibr_file_path)
      grub_free (hibr_file_path);
No need to check that argument to free is non-NULL.
    if (hibr_file)
      grub_file_close (hibr_file);

    return grub_errno;
}

static grub_extcmd_t cmd;

GRUB_MOD_INIT (nthibr)
{
    cmd = grub_register_extcmd ("nthibr", grub_cmd_nthibr, 0,
                                N_("DEVICE"),
                                N_("Test whether an NT system partition "
                                   "is hibernated."),
                                options);
}

GRUB_MOD_FINI (nthibr)
{
    grub_unregister_extcmd (cmd);
}

~Peter Lustig
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------------------------------

Message: 2
Date: Sat, 17 Dec 2011 12:39:41 +0100
From: Vladimir '?-coder/phcoder' Serbinenko     <address@hidden>
To:address@hidden
Subject: Re: New command to check NT's hibernation state
Message-ID:<address@hidden>
Content-Type: text/plain; charset=UTF-8; format=flowed


    /* Try to open 'hiberfil.sys' */
    hibr_file = grub_file_open (hibr_file_path);
    if (!hibr_file)
      {
        if (grub_errno == GRUB_ERR_FILE_NOT_FOUND)
          grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("'hiberfil.sys' not
found"));
This overriding is unnecessary. FS code already provides this message
This was intentional:  the default message ('file not found') is not
particularly helpful in this case since the
command's description nowhere mentions what file it's looking for (let
alone that any file is needed for it to
function).  I've updated this section to pop the first error off the
stack to eliminate the duplication (and added
a descriptive comment).
This means that your copy of GRUB is old. Newer ones do have the
descriptive message. And even if it wasn't the case it's something to be
fixed in FS code, not by replacing error message here.
I've been using the latest release (1.99), so this fix must still be on the development branch. But I do appreciate the idea of fixing something once at the source instead of at multiple points of consumption.

Attachment: nthibr.c
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