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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, 10 Dec 2011 01:03:50 -0500
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20111105 Thunderbird/8.0

On 12/3/2011 11:41 AM, Vladimir 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
   *  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<>.



/* 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}

No need for empty array. passing 0 instead of this array works.
I have tried it both ways. For some reason, passing the empty array works, but passing a null pointer doesn't. That is, when I try the latter, the options '-u' and '-h' are treated as regular arguments to the command.
static grub_err_t
grub_cmd_nthibr (grub_extcmd_context_t ctxt __attribute__ ((unused)),
                   int argc, char **args)
    grub_err_t status = GRUB_ERR_NONE;
    char *partition_name, *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)
        status = grub_error (GRUB_ERR_BAD_ARGUMENT,
                             N_("too few arguments specified"));
        goto exit;
    else if (argc>   1)
        status = grub_error (GRUB_ERR_BAD_ARGUMENT,
                             N_("too many arguments specified"));
        goto exit;

    partition_name = args[0];
    name_length = grub_strlen (partition_name);

    /* Check if partition specifier 'looks right' */
    if (partition_name[0] != '(' || partition_name[name_length - 1] != ')')
        status = grub_error (GRUB_ERR_BAD_FILENAME,
                             N_("invalid partition specifier"));
        goto exit;

I would recommend adding '(' and ')' if none found rather than giving error.
    /* Check if partition actually exists */
    partition_name[name_length - 1] = '\0';
    partition = grub_disk_open (partition_name + 1);
    if (!partition)
        status = grub_error (GRUB_ERR_UNKNOWN_DEVICE,
                             N_("partition not found"));
No need to run grub_error here. grub_disk_open already sets grub_errno
and grub_errmsg. Just status = grub_errno is enough.
        goto exit;
        grub_disk_close (partition);
        partition_name[name_length - 1] = ')';

No need for 'else' clause (goto already takes care of it)
    /* Build path to 'hiberfil.sys' */
    hibr_file_path = grub_malloc (grub_strlen (partition_name)
                                  + grub_strlen ("/hiberfil.sys") + 1);
    if (!hibr_file_path)
        status = grub_error (GRUB_ERR_OUT_OF_MEMORY,
                             N_("out of memory"));
        goto exit;
        grub_strcpy (hibr_file_path, partition_name);
        grub_strcat (hibr_file_path, "/hiberfil.sys");

Same here (no need for grub_error and else)
    /* Try to open 'hiberfil.sys' */
    hibr_file = grub_file_open (hibr_file_path);
    if (!hibr_file)
        status = grub_error (GRUB_ERR_FILE_NOT_FOUND,
                             N_("'hiberfil.sys' not found"));
        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)
        status = grub_error (GRUB_ERR_BAD_FILE_TYPE,
                             N_("'hiberfil.sys' too small"));
you need to conditionalize call to grub_error. if (!grub_errno) ...
since incomplete read may indicate an FS problem in which case you want
the original error message to remain.
        goto exit;

    /* Return SUCCESS if magic indicates file is active; else return FAILURE */
    if (!grub_strncasecmp ("hibr", hibr_file_magic, magic_size))
      grub_puts (N_("The system is hibernated."));
        grub_puts (N_("The system is NOT hibernated."));
        status = GRUB_ERR_TEST_FAILURE;

We also do grub_error (GRUB_ERR_TEST_FAILURE, "false");
    /* Ensure unmanaged resources are cleaned up */
    if (hibr_file_path)
      grub_free (hibr_file_path);
grub_free already checks for not-NULL pointers.
    if (hibr_file)
      grub_file_close (hibr_file);

    return status;
You can eliminate status and the need of keeping one by using return
I was unaware 'grub_errno' was used so extensively. Thanks for the tip: it definitely makes the logic cleaner.

I've followed all your recommendations (as far as possible). Here's the code again.

~Peter Lustig

Attachment: nthibr.c
Description: Text document

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