[v8] manual: add syscalls

Message ID xnmsnnrxzb.fsf@greed.delorie.com
State Superseded
Headers
Series [v8] manual: add syscalls |

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Commit Message

DJ Delorie June 14, 2024, 9:55 p.m. UTC
  [v8: macroize man page references, add pollfd]

The purpose of this patch is to add some system calls that (1) aren't
otherwise documented, and (2) are merely redirected to the kernel; and
define a standard way of doing so in the future.  A more detailed
explaination of how system calls are wrapped is added with reference
to the Linux Man-Pages project for further details.

Default version of man-pages is in configure.ac but can be overridden
by --with-man-pages=X.Y

Reviewed-by: Alejandro Colomar <alx@kernel.org>
  

Patch

diff --git a/config.make.in b/config.make.in
index 55e8b7563b..36096881b7 100644
--- a/config.make.in
+++ b/config.make.in
@@ -91,6 +91,7 @@  use-nscd = @use_nscd@
 build-hardcoded-path-in-tests= @hardcoded_path_in_tests@
 build-pt-chown = @build_pt_chown@
 pthread-in-libc = @pthread_in_libc@
+man-pages-version = @man_pages_version@
 
 # Build tools.
 CC = @CC@
diff --git a/configure b/configure
index 432e40a592..73ec5cdd66 100755
--- a/configure
+++ b/configure
@@ -706,6 +706,7 @@  force_install
 bindnow
 hardcoded_path_in_tests
 enable_timezone_tools
+man_pages_version
 rtld_early_cflags
 extra_nonshared_cflags
 sysheaders
@@ -787,6 +788,7 @@  with_headers
 with_nonshared_cflags
 with_rtld_early_cflags
 with_timeoutfactor
+with_man_pages
 enable_sanity_checks
 enable_shared
 enable_profile
@@ -1509,6 +1511,8 @@  Optional Packages:
                           build early initialization with additional CFLAGS
   --with-timeoutfactor=NUM
                           specify an integer to scale the timeout
+  --with-man-pages=VERSION
+                          tie manual to a specific man-pages version
   --with-cpu=CPU          select code for CPU variant
 
 Some influential environment variables:
@@ -4091,11 +4095,11 @@  if test x$ac_prog_cxx_stdcxx = xno
 then :
   { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $CXX option to enable C++11 features" >&5
 printf %s "checking for $CXX option to enable C++11 features... " >&6; }
-if test ${ac_cv_prog_cxx_cxx11+y}
+if test ${ac_cv_prog_cxx_11+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
-  ac_cv_prog_cxx_cxx11=no
+  ac_cv_prog_cxx_11=no
 ac_save_CXX=$CXX
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -4137,11 +4141,11 @@  if test x$ac_prog_cxx_stdcxx = xno
 then :
   { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $CXX option to enable C++98 features" >&5
 printf %s "checking for $CXX option to enable C++98 features... " >&6; }
-if test ${ac_cv_prog_cxx_cxx98+y}
+if test ${ac_cv_prog_cxx_98+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
-  ac_cv_prog_cxx_cxx98=no
+  ac_cv_prog_cxx_98=no
 ac_save_CXX=$CXX
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -4374,6 +4378,17 @@  fi
 printf "%s\n" "#define TIMEOUTFACTOR $timeoutfactor" >>confdefs.h
 
 
+man_pages_version=6.8
+
+
+# Check whether --with-man-pages was given.
+if test ${with_man_pages+y}
+then :
+  withval=$with_man_pages; man_pages_version=$withval
+fi
+
+
+
 # Check whether --enable-sanity-checks was given.
 if test ${enable_sanity_checks+y}
 then :
diff --git a/configure.ac b/configure.ac
index bdc385d03c..bdd82a8356 100644
--- a/configure.ac
+++ b/configure.ac
@@ -168,6 +168,15 @@  AC_ARG_WITH([timeoutfactor],
 	    [timeoutfactor=1])
 AC_DEFINE_UNQUOTED(TIMEOUTFACTOR, $timeoutfactor)
 
+man_pages_version=6.8
+
+AC_ARG_WITH([man-pages],
+	    AS_HELP_STRING([--with-man-pages=VERSION],
+			   [tie manual to a specific man-pages version]),
+	    [man_pages_version=$withval],
+	    [])
+AC_SUBST(man_pages_version)
+
 AC_ARG_ENABLE([sanity-checks],
 	      AS_HELP_STRING([--disable-sanity-checks],
 			     [really do not use threads (should not be used except in special situations) @<:@default=yes@:>@]),
diff --git a/manual/Makefile b/manual/Makefile
index b5fda4a7ae..a6c05db540 100644
--- a/manual/Makefile
+++ b/manual/Makefile
@@ -117,6 +117,7 @@  $(objpfx)stamp-pkgvers: $(common-objpfx)config.make
 	  echo "@set PKGVERSION_DEFAULT" >> $(objpfx)pkgvers-tmp; \
 	fi
 	echo "@set REPORT_BUGS_TO $(REPORT_BUGS_TEXI)" >> $(objpfx)pkgvers-tmp
+	echo "@set man_pages_version $(man-pages-version)" >> $(objpfx)pkgvers-tmp; \
 	echo "@end ifclear" >> $(objpfx)pkgvers-tmp
 	$(move-if-change) $(objpfx)pkgvers-tmp $(objpfx)pkgvers.texi
 	touch $@
diff --git a/manual/llio.texi b/manual/llio.texi
index fe1807a849..caaf001857 100644
--- a/manual/llio.texi
+++ b/manual/llio.texi
@@ -65,6 +65,7 @@  directly.)
 * Interrupt Input::                     Getting an asynchronous signal when
                                          input arrives.
 * IOCTLs::                              Generic I/O Control operations.
+* Other Low-Level I/O APIs::            Other low-level-I/O-related functions.
 @end menu
 
 
@@ -2214,6 +2215,8 @@  file descriptor, or until the timeout period expires.
 There is another example showing the use of @code{select} to multiplex
 input from multiple sockets in @ref{Server Example}.
 
+For an alternate interface to this functionality, see @code{poll}
+(@pxref{Other Low-Level I/O APIs}).
 
 @node Synchronizing I/O
 @section Synchronizing I/O operations
@@ -3297,7 +3300,9 @@  require additional arguments to be supplied.  These additional arguments
 and the return value and error conditions are given in the detailed
 descriptions of the individual commands.
 
-Briefly, here is a list of what the various commands are.
+Briefly, here is a list of what the various commands are.  For an
+exhaustive list of kernel-specific options, please see @xref{System
+Calls}.
 
 @vtable @code
 @item F_DUPFD
@@ -4633,5 +4638,28 @@  Most IOCTLs are OS-specific and/or only used in special system utilities,
 and are thus beyond the scope of this document.  For an example of the use
 of an IOCTL, see @ref{Out-of-Band Data}.
 
-@c FIXME this is undocumented:
-@c dup3
+@node Other Low-Level I/O APIs
+@section Other low-level-I/O-related functions
+
+@deftp {Data Type} {struct pollfd}
+@standards{POSIX.1,poll.h}
+@end deftp
+
+@deftp {Data Type} {struct epoll_event}
+@standards{Linux,sys/epoll.h}
+@end deftp
+
+@deftypefun int poll (struct pollfd *@var{fds}, nfds_t @var{nfds}, int @var{timeout})
+
+@manpagefunctionstub{poll,2}
+@end deftypefun
+
+@deftypefun int epoll_create(int @var{size})
+
+@manpagefunctionstub{epoll_create,2}
+@end deftypefun
+
+@deftypefun int epoll_wait(int @var{epfd}, struct epoll_event *@var{events}, int @var{maxevents}, int @var{timeout})
+
+@manpagefunctionstub{epoll_wait,2}
+@end deftypefun
diff --git a/manual/macros.texi b/manual/macros.texi
index 4a2e22f473..ce8c71d59f 100644
--- a/manual/macros.texi
+++ b/manual/macros.texi
@@ -282,4 +282,11 @@  cwd\comments\
 @macro standardsx {element, standard, header}
 @end macro
 
+@macro manpagefunctionstub {func,sec}
+This documentation is a stub.  For additional information on this
+function, consult the manual page
+@url{https://man7.org/linux/man-pages/man\sec\/\func\.\sec\.html}.
+@xref{System Calls}.
+@end macro
+
 @end ifclear
diff --git a/manual/socket.texi b/manual/socket.texi
index f0e35d9e13..66f893d219 100644
--- a/manual/socket.texi
+++ b/manual/socket.texi
@@ -41,6 +41,7 @@  aren't documented either so far.
 			   is to make it work with Inetd.
 * Socket Options::	Miscellaneous low-level socket options.
 * Networks Database::   Accessing the database of network names.
+* Other Socket APIs::   Other socket-related functions.
 @end menu
 
 @node Socket Concepts
@@ -3134,38 +3135,8 @@  You can use plain @code{recv} (@pxref{Receiving Data}) instead of
 treat all possible senders alike).  Even @code{read} can be used if
 you don't want to specify @var{flags} (@pxref{I/O Primitives}).
 
-@ignore
-@c sendmsg and recvmsg are like readv and writev in that they
-@c use a series of buffers.  It's not clear this is worth
-@c supporting or that we support them.
-@c !!! they can do more; it is hairy
-
-@deftp {Data Type} {struct msghdr}
-@standards{BSD, sys/socket.h}
-@end deftp
-
-@deftypefun ssize_t sendmsg (int @var{socket}, const struct msghdr *@var{message}, int @var{flags})
-@standards{BSD, sys/socket.h}
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-
-This function is defined as a cancellation point in multi-threaded
-programs, so one has to be prepared for this and make sure that
-allocated resources (like memory, files descriptors, semaphores or
-whatever) are freed even if the thread is cancel.
-@c @xref{pthread_cleanup_push}, for a method how to do this.
-@end deftypefun
-
-@deftypefun ssize_t recvmsg (int @var{socket}, struct msghdr *@var{message}, int @var{flags})
-@standards{BSD, sys/socket.h}
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-
-This function is defined as a cancellation point in multi-threaded
-programs, so one has to be prepared for this and make sure that
-allocated resources (like memory, files descriptors, semaphores or
-whatever) are freed even if the thread is canceled.
-@c @xref{pthread_cleanup_push}, for a method how to do this.
-@end deftypefun
-@end ignore
+If you need more flexibility and/or control over sending and receiving
+packets, see @code{sendmsg} and @code{recvmsg} (@pxref{Other Socket APIs}).
 
 @node Datagram Example
 @subsection Datagram Socket Example
@@ -3664,3 +3635,36 @@  returns a null pointer if there are no more entries.
 @c  libc_lock_unlock @aculock
 This function closes the networks database.
 @end deftypefun
+
+@node Other Socket APIs
+@section Other Socket APIs
+
+@deftp {Data Type} {struct msghdr}
+@standards{BSD, sys/socket.h}
+@end deftp
+
+@deftypefun ssize_t sendmsg (int @var{socket}, const struct msghdr *@var{message}, int @var{flags})
+@standards{BSD, sys/socket.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+
+@xref{System Calls} for information on this and other system calls.
+
+This function is defined as a cancellation point in multi-threaded
+programs, so one has to be prepared for this and make sure that
+allocated resources (like memory, files descriptors, semaphores or
+whatever) are freed even if the thread is cancel.
+@c @xref{pthread_cleanup_push}, for a method how to do this.
+@end deftypefun
+
+@deftypefun ssize_t recvmsg (int @var{socket}, struct msghdr *@var{message}, int @var{flags})
+@standards{BSD, sys/socket.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+
+@xref{System Calls} for information on this and other system calls.
+
+This function is defined as a cancellation point in multi-threaded
+programs, so one has to be prepared for this and make sure that
+allocated resources (like memory, files descriptors, semaphores or
+whatever) are freed even if the thread is canceled.
+@c @xref{pthread_cleanup_push}, for a method how to do this.
+@end deftypefun
diff --git a/manual/startup.texi b/manual/startup.texi
index 96a7a472bb..600f6abc3c 100644
--- a/manual/startup.texi
+++ b/manual/startup.texi
@@ -690,7 +690,34 @@  you don't need to know about it because you can just use @theglibc{}'s
 @code{chmod} function.
 
 @cindex kernel call
-System calls are sometimes called kernel calls.
+System calls are sometimes called syscalls or kernel calls, and this
+interface is mostly a purely mechanical translation from the kernel's
+ABI to the C ABI. For the set of syscalls where we do not guarantee
+POSIX Thread cancellation the wrappers only organize the incoming
+arguments from the C calling convention to the calling convention of
+the target kernel. For the set of syscalls where we provided POSIX
+Thread cancellation the wrappers set some internal state in the
+library to support cancellation, but this does not impact the
+behaviour of the syscall provided by the kernel.
+
+@Theglibc{} includes by reference the Linux man-pages
+@value{man_pages_version} documentation to document the listed
+syscalls for the Linux kernel. For reference purposes only the latest
+@uref{https://www.kernel.org/doc/man-pages/,Linux man-pages Project}
+documentation can be accessed from the
+@uref{https://www.kernel.org,Linux kernel} website. Where the syscall
+has more specific documentation in this manual that more specific
+documentation is considered authoritative.
+
+In some cases, if @theglibc{} detects that a system call has been
+superseded by a more capable one, the wrapper may map the old call to
+the new one.  For example, @code{dup2} is implemented via @code{dup3}
+by passing an additional empty flags argument, and @code{open} calls
+@code{openat} passing the additional @code{AT_FDCWD}.  Sometimes even
+more is done, such as converting between 32-bit and 64-bit time
+values.  In general, though, such processing is only to make the
+system call better match the C ABI, rather than change its
+functionality.
 
 However, there are times when you want to make a system call explicitly,
 and for that, @theglibc{} provides the @code{syscall} function.
@@ -712,6 +739,8 @@  we won't describe it here either because anyone who is coding
 library source code as a specification of the interface between them
 anyway.
 
+@code{syscall} does not provide cancellation logic, even if the system
+call you're calling is listed as cancellable above.
 
 @code{syscall} is declared in @file{unistd.h}.