sched_getattr.2: Update to include changed size semantics

Due to a userspace breakage, commit 1251201c0d34 ("sched/core: Fix
uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic
and code") changed the semantics of sched_getattr(2) when the
userspace struct is smaller than the kernel struct. Now, any
trailing non-zero data in the kernel structure is ignored when
copying to userspace. We also document the original error code
correctly (it was EFBIG not E2BIG) in the BUGS section.

Ref: 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
                 robustify sched_read_attr() ABI logic and code")

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man2/sched_setattr.2 b/man2/sched_setattr.2
index 2592a761a08679662b3806e68b8556f196c468d3..da0972a6a86d7de7a4723d16fab9667c98444acc 100644 (file)
--- a/man2/sched_setattr.2
+++ b/man2/sched_setattr.2
@@ -286,10 +286,8 @@ structure,
 the additional bytes in the user-space structure are not touched.
 If the caller-provided structure is smaller than the kernel
 .I sched_attr
-structure and the kernel needs to return values outside the provided space,
-.BR sched_getattr ()
-fails with the error
-.BR E2BIG .
+structure, the kernel will silently not return any values which would be stored
+outside the provided space.
 As with
 .BR sched_setattr (),
 these semantics allow for future extensibility of the interface.
@@ -416,6 +414,16 @@ failed with the error
 instead of
 .BR E2BIG
 for the case described in ERRORS.
+.PP
+In Linux versions up to 5.3,
+.BR sched_getattr ()
+failed with the error
+.BR EFBIG
+if the in-kernel
+.IR sched_attr
+structure was larger than the
+.IR size
+passed by user space.
 .\" In Linux versions up to up 3.15,
 .\" FIXME . patch from Peter Zijlstra pending
 .\" .BR sched_setattr ()