Date: Thu, 10 Mar 2011 12:10:58 -0800 From: mdf@FreeBSD.org To: John Baldwin <jhb@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: style(9) rules for nested includes Message-ID: <AANLkTikbRaCE628wJvKbBUbuBsJo6d6wJhvozSZA8kWW@mail.gmail.com> In-Reply-To: <201103101446.37589.jhb@freebsd.org> References: <AANLkTikqBJON46-EJFPPktT82L8dgX6dwwDrxWwFqumU@mail.gmail.com> <201103101446.37589.jhb@freebsd.org>
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On Thu, Mar 10, 2011 at 11:46 AM, John Baldwin <jhb@freebsd.org> wrote: > On Thursday, March 10, 2011 12:17:28 pm mdf@freebsd.org wrote: >> I recall a recent discussion/PR about nested includes in the context >> of <sys/linker_set.h> and <sys/queue.h> being a few of the only ones >> allowed. =A0However, I don't see anything in style(9) about this. > > bde@ is probably the most authoritative. =A0My understanding is that the = only > nested includes allowed in sys/sys/*.h are the two listed above and any h= eader > that starts with an underscore (sys/_mutex.h, etc.). =A0The underscore va= riants > were added to allow nested includes when absolutely necessary, but those > includes are the bare minimum required to define structures, etc. > >> Now we come to the reason I ask. =A0I'm working on a patch to change the >> static sysctl code to use the standard SYSININT/SYSUNINIT code rather >> than have special treatment in kern_linker.c, but to do this I need to >> either change quite a few places that include <sys/sysctl.h>, or >> include <sys/kernel.h> instead of <sys/linker_set.h> in sysctl.h, as >> the SI_SUB_SYSCTLS value isn't visible otherwise. > > Hmm, what is the reason to use SYSINIT's instead of a dedicated linker se= t? Mostly for consistency. The DB_COMMAND linker set was changed to use SYSINITs for version 8, and AFIAK SYSCTL is the only global kernel thing using a separate linker set. There's also a minor bug in initialization ordering where a static SYSCTL_PROC could use a lock initialized by SX_SYSINIT or MTX_SYSINIT, but at runtime module load the sysctl is exposed before the SI_SUB_LOCK stage has run, so in theory someone doing sysctl -a would crash the kernel on an attempt to lock an uninitialized mtx/sx. We saw this happen once at Isilon. Thanks, matthew
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