Re: [PATCH makedumpfile] makedumpfile: make reserve_diskspace do nothing for flattened format

["YAMAZAKI MASAMITSU(山崎 真光)" <yamazaki-msmt@nec.com>]

On 2024/07/19 17:00, HAGIO KAZUHITO(萩尾 一仁) wrote:
> Hi Jiri,
>
> sorry for the long delay.
>
> On 2024/06/19 21:04, Jiri Bohac wrote:
>> makedumpfile: make reserve_diskspace do nothing for flattened format
>>
>> reserve_diskspace() is called by write_elf_header() to make sure there is
>> always space to write the program header, even if writing other data fails
>> because of ENOSPC.
>>
>> This is harmful when writing the flattened format to STDOUT for two reasons:
>>
>> First, it actually wastes disk space, because first the block of zeroes is sent
>> to STDOUT by reserve_diskspace() and then the actual program header is sent,
>> meant to overwrite the zeroes when the flattened format is rearranged.
>>
>> Second, the algorithm used to read flattened format directly by the crash
>> program does not cope with the flattened file containing two chunks meant for
>> the same offset. It uses a binary search on a sorted array of flat_data headers
>> to find the data in the flat file. It may return the zeroed chunk written by
>> reserve_diskspace() near the beginning of the file instead of the actual ELF
>> header located near the end of the flattened file.
> Thank you for the patch, I found a vmcore that reproduced the issue:
>
> $ makedumpfile -FEd 31 vmcore > dump.FEd31
> $ crash vmlinux dump.FEd31
> ...
> realloc: No such file or directory
> cannot realloc resized ELF header buffer
> $
>
> and the patch fixed this, so
>
> Acked-by: Kazuhito Hagio <k-hagio-ab@nec.com>
>
> (Masa will apply the patch, please wait for a while.)
>
> Thanks,
> Kazu
>
>
>> Fixes: e39216fce9f73759509ec158e39c289e6c211125 ("Make the incomplete dumpfile generated by ENOSPC error analyzable.")
>> Signed-off-by: Jiri Bohac <jbohac@suse.cz>
>>
>> ---
>>    makedumpfile.c | 3 +++
>>    1 file changed, 3 insertions(+)
>>
>> diff --git a/makedumpfile.c b/makedumpfile.c
>> index cadc596..9624c3f 100644
>> --- a/makedumpfile.c
>> +++ b/makedumpfile.c
>> @@ -5206,6 +5206,9 @@ reserve_diskspace(int fd, off_t start_offset, off_t end_offset, char *file_name)
>>    
>>    	int ret = FALSE;
>>    
>> +	if (info->flag_flatten)
>> +		return TRUE;
>> +
>>    	assert(start_offset < end_offset);
>>    	buf_size = end_offset - start_offset;
>>    
Thank you, Jiri, for the patch. Sorry for the late apply the patch.

https://github.com/makedumpfile/makedumpfile/commit/c76301277552b95b613ffe9d5a211d01df73bd79

Thanks,
Masa
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