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

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

[Jiri Bohac]

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.

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;
 
-- 
2.43.0

-- 
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, Prague, Czechia


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

[HAGIO KAZUHITO(萩尾 一仁)]

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

[YAMAZAKI MASAMITSU(山崎 真光)]

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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