On Thu, 26 Aug 2021 at 03:26, 'Isabella Basso' via KUnit Development
<kunit-dev@xxxxxxxxxxxxxxxx> wrote:
> Keep function signatures minimal by making common definitions static.
> This does not change any behavior.
This seems like an odd change; if I read it right it's changing the
out-param passed to test_int_hash() to simply be static globals.
For one, it makes the code harder to read because now test_int_hash()
is no longer "pure" (no global side-effects ... modulo printfs), and
what was previously an out-param, is now a global.
Unfortunately this is poor style and likely to lead to hard-to-debug
problems. One such problem is if suddenly you have multiple threads
involved. While this is just a test and unlikely to be a problem, I
would recommend not introducing global state carelessly.
An alternative common idiom, where a set of variables are always
passed around to other functions, is to introduce a struct and pass a
pointer to it along.
> Signed-off-by: Isabella Basso <isabellabdoamaral@xxxxxx>
> ---
> lib/test_hash.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/lib/test_hash.c b/lib/test_hash.c
> index d4b0cfdb0377..8bcc645a7294 100644
> --- a/lib/test_hash.c
> +++ b/lib/test_hash.c
> @@ -23,6 +23,11 @@
> #include <linux/stringhash.h>
> #include <linux/printk.h>
>
> +#define SIZE 256 /* Run time is cubic in SIZE */
> +
> +static u32 string_or; /* stores or-ed string output */
> +static u32 hash_or[2][33] = { { 0, } }; /* stores or-ed hash output */
These now use up memory for as long as this module is loaded, vs.
before where it would only use up stack space. (For a test that's not
a problem, but in non-test code it might.)
> /* 32-bit XORSHIFT generator. Seed must not be zero. */
> static u32 __init __attribute_const__
> xorshift(u32 seed)
> @@ -66,7 +71,7 @@ fill_buf(char *buf, size_t len, u32 seed)
> * recompile and re-test the module without rebooting.
> */
> static bool __init
> -test_int_hash(unsigned long long h64, u32 hash_or[2][33])
> +test_int_hash(unsigned long long h64)
> {
> int k;
> u32 h0 = (u32)h64, h1, h2;
> @@ -123,17 +128,15 @@ test_int_hash(unsigned long long h64, u32 hash_or[2][33])
> return true;
> }
>
> -#define SIZE 256 /* Run time is cubic in SIZE */
> -
> static int __init
> test_hash_init(void)
> {
> char buf[SIZE+1];
> - u32 string_or = 0, hash_or[2][33] = { { 0, } };
> unsigned tests = 0;
> unsigned long long h64 = 0;
> int i, j;
>
> + string_or = 0;
That's another problem with changes like this; now the compiler has no
chance to warn you in case the variable is not initialized correctly.
Also, I don't see string_or used anywhere else. Why make it global?
If a later change would require that, it should say so in the commit
message. But my guess is you can avoid all that by bundling everything
up in a struct.
> fill_buf(buf, SIZE, 1);
>
> /* Test every possible non-empty substring in the buffer. */
> @@ -161,7 +164,7 @@ test_hash_init(void)
>
> string_or |= h0;
> h64 = h64 << 32 | h0; /* For use with hash_64 */
> - if (!test_int_hash(h64, hash_or))
> + if (!test_int_hash(h64))
> return -EINVAL;
> tests++;
> } /* i */
> --
> 2.33.0
>
> --
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