From 3eff6a3e574c2f704f9be1f4867c3d0b3d804435 Mon Sep 17 00:00:00 2001 From: Zijun Hu Date: Mon, 7 Apr 2025 19:44:16 +0800 Subject: [PATCH] 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: Zijun Hu Reviewed-by: Jeff Layton Signed-off-by: Andrew Morton --- lib/errseq.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/lib/errseq.c b/lib/errseq.c index 93e9b94358dc6..13a2581c5a878 100644 --- a/lib/errseq.c +++ b/lib/errseq.c @@ -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; } -- 2.47.2