Module Name: src
Committed By: riastradh
Date: Wed Mar 26 14:12:16 UTC 2025
Modified Files:
src/share/man/man3: CMSG_DATA.3
Log Message:
cmsg(3): Clarify guarantees about CMSG_SPACE/LEN constancy.
Add some line breaks while here to break up walls of text so it's
easier to compare the two paragraphs and see how CMSG_SPACE is meant
for struct msghdr::msg_controllen and CMSG_LEN is meant for struct
cmsghdr::cmsg_len.
PR lib/59054: cmsg(3) uses malloc(3) unnecessarily
To generate a diff of this commit:
cvs rdiff -u -r1.5 -r1.6 src/share/man/man3/CMSG_DATA.3
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/share/man/man3/CMSG_DATA.3
diff -u src/share/man/man3/CMSG_DATA.3:1.5 src/share/man/man3/CMSG_DATA.3:1.6
--- src/share/man/man3/CMSG_DATA.3:1.5 Sat Feb 8 13:30:42 2025
+++ src/share/man/man3/CMSG_DATA.3 Wed Mar 26 14:12:16 2025
@@ -1,4 +1,4 @@
-.\" $NetBSD: CMSG_DATA.3,v 1.5 2025/02/08 13:30:42 riastradh Exp $
+.\" $NetBSD: CMSG_DATA.3,v 1.6 2025/03/26 14:12:16 riastradh Exp $
.\" $OpenBSD: CMSG_DATA.3,v 1.5 2008/03/24 16:11:07 deraadt Exp $
.\" Written by Jared Yanovich <[email protected]>
.\" Public domain, July 3, 2005
@@ -64,12 +64,19 @@ This routine determines the size in byte
which includes the control message header.
.Fa len
specifies the length of the data held by the control message.
+.Pp
This value is what is normally stored in the
.Fa cmsg_len
of each control message.
+.Pp
This routine accounts for any alignment constraints on the beginning of
ancillary data.
-This macro might not evaluate to a compile-time constant.
+.Pp
+If
+.Fa len
+is an integer constant expression, then
+.Fn CMSG_LEN len
+is an integer constant expression.
.It Fn CMSG_NXTHDR mhdr cmsg
This routine returns the location of the control message following
.Fa cmsg
@@ -84,11 +91,18 @@ This routine determines the size in byte
message and its contents of length
.Fa len ,
which includes the control message header.
+.Pp
This value is what is normally stored in
.Fa msg_msgcontrollen .
+.Pp
This routine accounts for any alignment constraints on the beginning of
ancillary data as well as any needed to pad the next control message.
-This macro might not evaluate to a compile-time constant.
+.Pp
+If
+.Fa len
+is an integer constant expression, then
+.Fn CMSG_SPACE len
+is an integer constant expression.
.El
.Sh EXAMPLES
The following example constructs a control message containing a file
