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errseq: eliminate special limitation for macro MAX_ERRNO

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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: Zijun Hu <quic_zijuhu@quicinc.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zijun Hu 2025-04-07 19:44:16 +08:00 • committed by Andrew Morton
parent ae5b350085
commit 3eff6a3e57
1 changed files with 7 additions and 6 deletions
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13
lib/errseq.c
View file

@ -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;
}