Commit 3eff6a3e authored by Zijun Hu's avatar Zijun Hu Committed by Andrew Morton
Browse files

errseq: eliminate special limitation for macro MAX_ERRNO 

Current errseq implementation depends on a very special precondition that
macro MAX_ERRNO must be (2^n - 1).

Eliminate the limitation by

- redefining macro ERRSEQ_SHIFT
- defining a new macro ERRNO_MASK instead of MAX_ERRNO for errno mask.

There is no plan to change the value of MAX_ERRNO, but this makes the
implementation more generic and eliminates the BUILD_BUG_ON().

Link: https://lkml.kernel.org/r/20250407-improve_errseq-v1-1-7b27cbeb8298@quicinc.com


Signed-off-by: default avatarZijun Hu <quic_zijuhu@quicinc.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent ae5b3500

lib/errseq.c

+7 −6
Original line number Diff line number Diff line
@@ -34,11 +34,14 @@ 
 */



/* The low bits are designated for error code (max of MAX_ERRNO) */

#define ERRSEQ_SHIFT		ilog2(MAX_ERRNO + 1)

#define ERRSEQ_SHIFT		(ilog2(MAX_ERRNO) + 1)



/* This bit is used as a flag to indicate whether the value has been seen */

#define ERRSEQ_SEEN		(1 << ERRSEQ_SHIFT)



/* Leverage macro ERRSEQ_SEEN to define errno mask macro here */

#define ERRNO_MASK		(ERRSEQ_SEEN - 1)



/* The lowest bit of the counter */

#define ERRSEQ_CTR_INC		(1 << (ERRSEQ_SHIFT + 1))
@@ -60,8 +63,6 @@ errseq_t errseq_set(errseq_t *eseq, int err) 
{

	errseq_t cur, old;



	/* MAX_ERRNO must be able to serve as a mask */

	BUILD_BUG_ON_NOT_POWER_OF_2(MAX_ERRNO + 1);



	/*

	 * Ensure the error code actually fits where we want it to go. If it
@@ -79,7 +80,7 @@ errseq_t errseq_set(errseq_t *eseq, int err) 
		errseq_t new;



		/* Clear out error bits and set new error */

		new = (old & ~(MAX_ERRNO|ERRSEQ_SEEN)) | -err;

		new = (old & ~(ERRNO_MASK | ERRSEQ_SEEN)) | -err;



		/* Only increment if someone has looked at it */

		if (old & ERRSEQ_SEEN)
@@ -148,7 +149,7 @@ int errseq_check(errseq_t *eseq, errseq_t since) 


	if (likely(cur == since))

		return 0;

	return -(cur & MAX_ERRNO);

	return -(cur & ERRNO_MASK);

}

EXPORT_SYMBOL(errseq_check);
@@ -200,7 +201,7 @@ int errseq_check_and_advance(errseq_t *eseq, errseq_t *since) 
		if (new != old)

			cmpxchg(eseq, old, new);

		*since = new;

		err = -(new & MAX_ERRNO);

		err = -(new & ERRNO_MASK);

	}

	return err;

}