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

[Coiby Xu]

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