git: c724b26acd59 - stable/15 - exterror: advertise error strings via kern.features.exterr_strings

The branch stable/15 has been updated by netchild:

URL: https://cgit.FreeBSD.org/src/commit/?id=c724b26acd59fe5078c5e64e707303ef9c2c522c

commit c724b26acd59fe5078c5e64e707303ef9c2c522c
Author:     Alexander Leidinger <[email protected]>
AuthorDate: 2026-07-21 20:39:56 +0000
Commit:     Alexander Leidinger <[email protected]>
CommitDate: 2026-07-28 10:04:41 +0000

    exterror: advertise error strings via kern.features.exterr_strings
    
    Allow userland, in particular test cases for EXTERROR conversions,
    to detect at run time whether extended errors include the
    descriptive message strings, which depends on the EXTERR_STRINGS
    kernel option and cannot be probed in any other way.
    
    Reviewed by:            kib
    MFC after:              1 week
    Assisted-by:            Claude Code (Fable 5)
    Differential Revision:  https://reviews.freebsd.org/D58321
    
    (cherry picked from commit c8db6d4b63f18c81557628ad0d3f715bea46cc99)
---
 share/man/man9/exterror.9 | 13 ++++++++++++-
 sys/kern/sys_generic.c    |  4 ++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/share/man/man9/exterror.9 b/share/man/man9/exterror.9
index 47ffda065d43..2c9dc73f7616 100644
--- a/share/man/man9/exterror.9
+++ b/share/man/man9/exterror.9
@@ -6,7 +6,7 @@
 .\" Konstantin Belousov <[email protected]> under sponsorship
 .\" from the FreeBSD Foundation.
 .\"
-.Dd November 5, 2025
+.Dd July 21, 2026
 .Dt EXTERROR 9
 .Os
 .Sh NAME
@@ -171,6 +171,17 @@ were modified to print the extended information if it is available
 in addition to the usual
 .Va errno
 decoding.
+.Pp
+Kernels built with the
+.Cd option EXTERR_STRINGS
+advertise the
+.Va kern.features.exterr_strings
+.Xr sysctl 8
+variable, see
+.Xr feature_present 3 ,
+indicating that the reported errors include the descriptive message strings.
+Without it, only the numeric information (error code, category,
+source line number and parameters) is available.
 .Sh ASYNCHRONOUS INPUT/OUTPUT
 Due to the nature of the
 .Fx
diff --git a/sys/kern/sys_generic.c b/sys/kern/sys_generic.c
index 1b88581714d2..b829a70f26aa 100644
--- a/sys/kern/sys_generic.c
+++ b/sys/kern/sys_generic.c
@@ -112,6 +112,10 @@ static MALLOC_DEFINE(M_IOCTLOPS, "ioctlops", "ioctl data buffer");
 static MALLOC_DEFINE(M_SELECT, "select", "select() buffer");
 MALLOC_DEFINE(M_IOV, "iov", "large iov's");
 
+#ifdef EXTERR_STRINGS
+FEATURE(exterr_strings, "Extended error reporting includes message strings");
+#endif
+
 static int	pollout(struct thread *, struct pollfd *, struct pollfd *,
 		    u_int);
 static int	pollscan(struct thread *, struct pollfd *, u_int);