Module Name: src
Committed By: uwe
Date: Sun Jul 9 00:29:49 UTC 2023
Modified Files:
src/share/man/man9: versioningsyscalls.9
Log Message:
versioningsyscalls(9): markup fixes
While here, fix the pasto for the new ino_t and time_t size.
To generate a diff of this commit:
cvs rdiff -u -r1.1 -r1.2 src/share/man/man9/versioningsyscalls.9
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/man9/versioningsyscalls.9
diff -u src/share/man/man9/versioningsyscalls.9:1.1 src/share/man/man9/versioningsyscalls.9:1.2
--- src/share/man/man9/versioningsyscalls.9:1.1 Sat Jul 8 16:14:11 2023
+++ src/share/man/man9/versioningsyscalls.9 Sun Jul 9 00:29:49 2023
@@ -1,4 +1,4 @@
-.\" $NetBSD: versioningsyscalls.9,v 1.1 2023/07/08 16:14:11 christos Exp $
+.\" $NetBSD: versioningsyscalls.9,v 1.2 2023/07/09 00:29:49 uwe Exp $
.\"
.\" Copyright (c) 2023 The NetBSD Foundation, Inc.
.\" All rights reserved.
@@ -28,11 +28,13 @@
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd June 23, 2023
-.Dt versioningsyscalls 9
+.Dt VERSIONINGSYSCALLS 9
.Os
+.
.Sh NAME
.Nm versioningsyscalls
.Nd guide on versioning syscalls
+.
.Sh DESCRIPTION
.Nx
has the ability to change the ABI of a syscall whilst retaining backwards
@@ -45,18 +47,18 @@ to move from 16 bits to 32 bits,
.Ft ino_t
and
.Ft time_t
-to move from 16 bits to 32 bits and
-adding fields to
+to move from 32 bits to 64 bits,
+and adding fields to
.Ft struct kevent
without disturbing existing binaries.
To achieve this both kernel and userland changes are required.
.Pp
In the kernel, a new syscall is added with a new ABI, and the old syscall
is retained and moved to a new location that holds the compatibility syscalls
-.Pa ( src/sys/compat ) .
+.Pq Pa src/sys/compat .
Kernels can be compiled with or without backwards compatibility syscalls.
See the
-.Li COMPAT_XX
+.Dv COMPAT_ Ns Ar XX
options in
.Xr options 4 .
.Pp
@@ -76,18 +78,18 @@ emulated because of the cost and safety
.Pp
To avoid confusion, the following words are used to disambiguate which version
of the system call is being described.
-.Bl -tag -offset indent -width "current"
-.It old
+.Bl -tag -offset indent -width Em
+.It Em old
Any previous versions of the syscall, which have already been versioned and
superseded by the current version of the syscall.
-.It current
+.It Em current
The version of the syscall currently in use.
-.It next
+.It Em next
The version of the syscall that will become standard in the next release.
.El
.Pp
Additionally,
-.Em XYZ
+.Ar XYZ
always represents the last
.Nx
release where the current
@@ -96,63 +98,71 @@ leading zero.
For example
.Nx 0.9
has
-.Li COMPAT_09
+.Dv COMPAT_09
whereas
.Nx 10.0
has
-.Li COMPAT_100 .
+.Dv COMPAT_100 .
+.
.Sh VERSIONING THE SYSCALL
This section describes what needs to be modified to add the new version of the
syscall.
It assumes the current version of the syscall is
-.Fn my_syscall struct\ my_struct\ *ms
+.Fn my_syscall "struct my_struct *ms"
and that
-.Li my_struct
+.Ft my_struct
will be versioned.
If not versioning a struct, passages that mention
-.Li my_struct
+.Ft my_struct
can be ignored.
+.
.Ss Versioning structs
To version
-.Li struct my_struct ,
+.Ft struct my_struct ,
first make a copy of
-.Li my_struct
+.Ft my_struct
renamed to
-.Li my_structXYZ
+.Ft my_structXYZ
in an equivalent header in
.Pa sys/compat/sys .
After that, you can freely modify
-.Li my_struct
+.Ft my_struct
as desired.
+.
.Ss Versioning the entry point
The stub for the next version of the syscall will be
.Fn __my_syscallXYZ ,
and will have entry point
.Fn sys___my_syscallXYZ .
+.
.Ss Modifying syscalls.conf
.Pa sys/kern/syscalls.conf
may need to be modified to contain
.Li compat_XYZ
in the
-.Li compatopts
-field.
+.Va compatopts
+variable.
+.
.Ss Modifying syscalls.master
First, add the next syscall to
.Pa sys/kern/syscalls.master
keeping
-.Li my_syscall
-as the name, and set the (optional) compat field of the declaration to XYZ.
+.Fn my_syscall
+as the name, and set the (optional) compat field of the declaration to
+.Ar XYZ .
.Pp
Next, modify the current version of the syscall, and replace the type
-field (usually just STD) with
-.Li COMPAT_XYZ MODULAR compat_XYZ .
+field
+.Pq usually just Li STD
+with
+.Dv COMPAT_XYZ MODULAR compat_XYZ .
.Pp
The keyword
-.Li MODULAR
+.Dv MODULAR
indicates that the system call can be part of a kernel module.
Even if the system call was not part of a module before, now it will be part
of the
-.Li COMPAT_XYZ
+.Dv COMPAT_XYZ
module.
.Pp
Finally, if applicable, replace the types of the current and old versions of the
@@ -162,27 +172,29 @@ Overall, the final diff should look like
.Bd -literal
- 123 STD { int|sys||my_syscall(struct my_struct *ms); }
+ 123 COMPAT_XYZ MODULAR compat_XYZ { int|sys||my_syscall(struct my_structXYZ *ms); }
-\&.\&.\&.
+\&...
+ 456 STD { int|sys|XYZ|my_syscall(struct my_struct *ms); }
.Ed
+.
.Ss Modifying Makefile.rump
If the current syscall is rump,
.Pa sys/rump/Makefile.rump
must contain
-.Li XYZ
+.Ar XYZ
in the
-.Li RUMP_NBCOMPAT
+.Dv RUMP_NBCOMPAT
variable.
+.
.Ss Regenerating the system calls
If versioning structs, then modify
.Pa sys/kern/makesyscalls.sh
by adding and entry for
-.Li struct my_structXYZ
+.Ft struct my_structXYZ
type to
-.Li uncompattypes .
+.Va uncompattypes .
.Pp
The
-.Li uncompattypes
+.Va uncompattypes
map is used in
.Xr rump 7
system call table generation, to map from the versioned types to the original
@@ -198,6 +210,7 @@ and then running
.Pa sys/rump/makerumpsyscalls.sh
passing it the path to the result of the build you just did as its first
argument.
+.
.Sh KERNEL COMPATIBILITY
This section covers maintaining compatibility at the kernel level, by
adding an entry point for the current syscall in an appropriate compat
@@ -207,6 +220,7 @@ syscall has entry point
.Fn sys_my_syscall
and lives inside
.Pa sys/kern/my_file.c .
+.
.Ss Creating the compat current syscall
The compat version of the current syscall has entry point
.Fn compat_XYZ_sys_my_syscall ,
@@ -215,6 +229,7 @@ and should be implemented in
with the same semantics as the current syscall.
Often this involves translating the arguments to the next syscall,
and then calling that syscall's entry point.
+.
.Ss Adding it to the compat module
.Pa sys/compat/common/my_file_XYZ.c
must contain an array of
@@ -239,24 +254,25 @@ The stubs for these functions should be
.Pp
Overall,
.Pa sys/compat/common/my_file_XYZ.c
-must at the minimum include
-.Bd -literal
-+ static const struct syscall_package my_file_XYZ_syscalls[] = {
-+ { SYS_compat_XYZ_my_syscall, 0, (sy_call_t *)compat_XYZ_sys_my_syscall },
-+ { 0, 0, NULL },
-+ };
-+
-+ int
-+ compat_XYZ_my_syscall(...)
-+ { /* Compat implementation goes here. */ }
-+
-+ int
-+ my_file_XYZ_init(void)
-+ { return syscall_establish(NULL, my_file_XYZ_syscalls); }
-+
-+ int
-+ my_file_XYZ_fini(void)
-+ { return syscall_disestablish(NULL, my_file_XYZ_syscalls); }
+must at the minimum contain
+.Bd -literal -offset indent
+static const struct syscall_package my_file_XYZ_syscalls[] = {
+ { SYS_compat_XYZ_my_syscall, 0,
+ (sy_call_t *)compat_XYZ_sys_my_syscall },
+ { 0, 0, NULL },
+};
+
+int
+compat_XYZ_my_syscall(...)
+{ /* Compat implementation goes here. */ }
+
+int
+my_file_XYZ_init(void)
+{ return syscall_establish(NULL, my_file_XYZ_syscalls); }
+
+int
+my_file_XYZ_fini(void)
+{ return syscall_disestablish(NULL, my_file_XYZ_syscalls); }
.Ed
.Pp
Finally,
@@ -268,7 +284,9 @@ and
functions call
.Fn my_file_XYZ_init
and
-.Fn my_file_XYZ_fini .
+.Fn my_file_XYZ_fini
+respectively.
+.
.Ss Modifying old compat syscalls
If the current syscall has already been versioned, you might need to
modify the old compat syscalls in
@@ -277,9 +295,11 @@ to either use the next syscall or the cu
Note that compat code can be made to depend on compat code for more
recent releases.
.Sh USERLAND COMPATIBILITY
-With the exception of the libraries described below, making the rest of userland
-work will just involve recompiling, and perhaps changing a constant or a
+With the exception of the libraries described below, making the rest
+of userland work will just involve recompiling, and perhaps changing a
+constant or a
.Li #define .
+.
.Ss libc
A userland version of any old and current versions of the syscall should be
implemented in terms of the next syscall in
