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


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