Date: Tue, 22 Sep 2009 11:28:48 +0400 From: Igor Sysoev <is@rambler-co.ru> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-hackers@freebsd.org, d@delphij.net Subject: Re: fcntl(F_RDAHEAD) Message-ID: <20090922072848.GA727@rambler-co.ru> In-Reply-To: <20090921112909.GQ47688@deviant.kiev.zoral.com.ua> References: <20090917101526.GF57619@rambler-co.ru> <4AB2B7A1.5000601@delphij.net> <20090918074027.GI47688@deviant.kiev.zoral.com.ua> <20090921111245.GB23958@rambler-co.ru> <20090921112909.GQ47688@deviant.kiev.zoral.com.ua>
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On Mon, Sep 21, 2009 at 02:29:09PM +0300, Kostik Belousov wrote: > On Mon, Sep 21, 2009 at 03:12:45PM +0400, Igor Sysoev wrote: > > > What I dislike about the patch is the new kernel-private flag that is > > > eaten from the open(2) flags namespace. We do already have FHASLOCK, > > > so far the only such flag. > > > > We can change > > int f_seqcount; > > to > > u_int f_seqcount; > > > > and can use highest bit instead of O_READAHEAD: anyway f_seqcount is shifted > > to 16 bits left. > > Or do the same trick as was done for FHASLOCK and override some flag that > is not saved after open, see FMASK. > > Or split f_seqcount into two u_short fields, one for f_seqcount, second for > f_kflag, and use the later for FHASLOCK and FREADAHEAD. [We are trying to > not grow struct file unless absolutely neccessary]. I agree that struct file should not grow (at least in this case). However, I believe splitting f_seqcount into two fields will break kernel ABI. Or not ? I think f_seqcount should be splitted in 9-CURRENT and probably, in 8-STABLE, but in 7-STABLE we may use the open(2) flags namespace. -- Igor Sysoev http://sysoev.ru/en/
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