[PATCH v3] getrlimit.2: old_getrlimit/ugetrlimit and RLIM_INFINITY discrepancies

Eugene Syromyatnikov
2021-07-29T15:44:11Z

Historically, Linux didn't follow SUS with respect to RLIM_INFINITY
signedness; it was changed during 2.4 development cycle, but in somewhat
peculiar and arch-dependent fashion due to backward compatibility
concerns.

Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
---
man2/getrlimit.2 | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

diff --git a/man2/getrlimit.2 b/man2/getrlimit.2
index 648fd3c..5a360d4 100644
--- a/man2/getrlimit.2
+++ b/man2/getrlimit.2
@@ -646,6 +646,37 @@ The name of the glibc wrapper function is
.BR prlimit ();
the underlying system call is
.BR prlimit64 ().
+The corresponding infinity value constant is provided in
+.I <linux/resource.h>
+as
+.BR RLIM64_INFINITY.
+.PP
+Original Linux implementation used signed types for limits; that was changed
+(along with the value of the
+.B RLIM_INFINITY
+constant)
+.\" http://repo.or.cz/davej-history.git/blobdiff/129f8758d8c41e0378ace0b6e2f56bbb8a1ec694..15305d2e69c3a838bacd78962c07077d2821f255:/include/linux/resource.h
+during 2.4 development cycle, as it wasn't compatible
+with Single UNIX Specification.
+However, in order to preserve backward compatibility, the routine
+.IR sys_old_getrlimit
+has been implemented under
+.B __NR_getrlimit
+syscall slot, with infinity checks being performed against hard-coded 0x7fffffff
+value, and the routine
+.I sys_getrlimit
+has been exposed under a new name,
+.BR ugetrlimit ().
+Note that most newer architectures don't have the latter, with
+.BR getrlimit ()
+providing proper implementation.
+Also worth noting that several architectures decided not to change
+.B RLIM_INFINITY
+value: 32-bit mips and sparc (but not 64-bit variants, that switched
+to the new value of (~0UL)) retained the old 0x7fffffff value,
+and alpha retained 0x7ffffffffffffffful.
+.\" ...along with a request to call when one runs into it:
+.\" https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/alpha/include/uapi/asm/resource.h#n15
.SH BUGS
In older Linux kernels, the
.B SIGXCPU
--
2.1.4