Date: Tue, 18 Nov 2025 05:35:14 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: c0a38339fec3 - main - exterror.9: explain buffers and bios usage of extended errors Message-ID: <202511180535.5AI5ZE5Z080106@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=c0a38339fec37a5b6367f138f059a12d6d716fd4 commit c0a38339fec37a5b6367f138f059a12d6d716fd4 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2025-11-18 04:23:41 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2025-11-18 05:34:56 +0000 exterror.9: explain buffers and bios usage of extended errors Reviewed by: pauamma_gundo.com Sponsored by: The FreeBSD Foundation Differential revision: https://reviews.freebsd.org/D53798 --- share/man/man9/exterror.9 | 82 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 82 insertions(+) diff --git a/share/man/man9/exterror.9 b/share/man/man9/exterror.9 index 79197e4a187d..fd4b732b8213 100644 --- a/share/man/man9/exterror.9 +++ b/share/man/man9/exterror.9 @@ -17,8 +17,15 @@ #define EXTERR_CATEGORY EXTERR_CAT_MYCATEGORY .Ed .In sys/exterrvar.h +.Vt struct kexterr; +.Ft void +.Fn exterr_clear "struct kexterr *ke" +.Ft int +.Fn exterr_set_from "const struct kexterr *ke" .Ft int .Fn EXTERROR "int error" "const char *msg" ... +.Ft void +.Fn EXTERROR_KE "struct kexterr *ke" "int error" "const char *msg" ... .Sh DESCRIPTION The .Nm @@ -102,6 +109,33 @@ Additionally, use of .Fn EXTERROR in kernel threads is not sensible as there is no userspace to retrieve the extended error data. +.Pp +The +.Fn EXTERROR_KE +macro is similar to +.Fn EXTERROR , +but it takes an explicit pointer +.Fa kep +to the +.Vt struct kexterr +to fill with the extended error information. +The macro expression value is +.Vt void . +See below for description of the asynchronous i/o error facilities. +.Pp +The +.Fn exterr_clear +function clears the content of the +.Vt struct kexterr +pointed to by the argument +.Fa ke . +.Pp +The +.Fn exterr_set_from +function sets the current thread extended error data from the +.Fa struct kexterr +pointed to by the argument +.Fa ke . .Sh USERSPACE ACCESS TO EXTENDED ERROR DATA There is no syscall overhead for using .Nm @@ -127,6 +161,54 @@ were modified to print the extended information if it is available in addition to the usual .Va errno decoding. +.Sh ASYNCHRONOUS INPUT/OUTPUT +Due to the nature of the +.Fx +i/o subsystem, most input/output requests, presented as buffers (as in +.Vt struct buf ) +and geom bio's ( +.Vt struct bio ) +are processed asynchronously in filesystem- and geom-private threads. +This makes it challenging to pass any extended error information +from the geom providers and drivers, where an error typically occurs, +back to the thread that initiated the request, and is the consumer of +the result. +.Pp +To alleviate the mismatch, both +.Vt struct buf +and +.Vt struct bio +have member of the +.Vt struct kexterr +type. +For buffers, the +.Va b_exterr +for +.Vt struct buf , +and +.Va bio_exterr +for +.Vt struct bio . +Asynchronous i/o code can use the +.Fn EXTERROR_KE +macro, passing the pointer to the current request's embedded +.Vt struct kexterr , +to record the extended error. +In both cases, the +.Va BIO_EXTERR +flag should be set to indicate that whole extended error is valid, +not only the +.Va b_error +or +.Va bio_error +values. +.Pp +Both VFS and geom generic layers, and several geom providers that generate +subordinate bio's from the original request, are aware of the extended +errors. +They pass +.Vt kexterr +from the failed request back to the thread that create the request. .Sh SEE ALSO .Xr errno 3 , .Xr err 3help
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