Re: [PATCH v4 2/7] crash_dump: make dm crypt keys persist for the kdump kernel

Coiby Xu
2024-06-07T12:28:31Z

On Wed, Jun 05, 2024 at 04:22:12PM +0800, Baoquan He wrote:
>On 05/23/24 at 01:04pm, Coiby Xu wrote:
>.....
>> diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
>> new file mode 100644
>> index 000000000000..78809189084a
>> --- /dev/null
>> +++ b/kernel/crash_dump_dm_crypt.c
>> @@ -0,0 +1,113 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
[...]
>> +
>> +static unsigned int key_count;
>> +static size_t keys_header_size;
>
>These two global variables seems not so necessary. Please see comment at
>below.

Thanks for the comment! But I think it's better to keep these two static
variables for reasons as will be explained later.

>
>> +
>> +struct dm_crypt_key {
>> + unsigned int key_size;
>> + char key_desc[KEY_DESC_LEN];
>> + u8 data[KEY_SIZE_MAX];
>> +};
>> +
>> +static struct keys_header {
>> + unsigned int key_count;
> ~~~~~~~~
> This is the max number a system have from init();
>You can add one field member to record how many key slots have been
>used.
>> + struct dm_crypt_key keys[] __counted_by(key_count);
>> +} *keys_header;
>
>Maybe we can rearrange the keys_header like below, the name may not be
>very appropriate though.
>
>static struct keys_header {
> unsigned int max_key_slots;
> unsigned int used_key_slots;
> struct dm_crypt_key keys[] __counted_by(key_count);
>} *keys_header;

Thanks for the suggestion! Since 1) KEY_NUM_MAX already defines the
maximum number of dm crypt keys 2) we only need to let the kdump kernel
now how many keys are saved, so I simply use total_keys instead of
key_count in struct keys_header in v5,

static struct keys_header {
unsigned int total_keys;
struct dm_crypt_key keys[] __counted_by(total_keys);
} *keys_header;

Hopefully this renaming will improve code readability.

>
>>
>
>> +
>> +static size_t get_keys_header_size(struct keys_header *keys_header,
>> + size_t key_count)
>> +{
>> + return struct_size(keys_header, keys, key_count);
>> +}
>
>I personally don't think get_keys_header_size is so necessary. If we
>have to keep it, may be we can remove the global variable
>keys_header_size, we can call get_keys_header_size() and use local
>variable to record the value instead.

Thanks for the suggestion! But the kdump kernel also need to call
get_keys_header_size in later patches.

--
Best regards,
Coiby