Date: Mon, 19 May 2008 10:15:34 -0400 From: John Baldwin <jhb@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-arch@freebsd.org Subject: Re: Per-open file private data for the cdevs Message-ID: <200805191015.35212.jhb@freebsd.org> In-Reply-To: <20080515123055.GY18958@deviant.kiev.zoral.com.ua> References: <20080504171002.GN18958@deviant.kiev.zoral.com.ua> <200805150730.08418.jhb@freebsd.org> <20080515123055.GY18958@deviant.kiev.zoral.com.ua>
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On Thursday 15 May 2008 08:30:55 am Kostik Belousov wrote: > On Thu, May 15, 2008 at 07:30:07AM -0400, John Baldwin wrote: > > On Wednesday 14 May 2008 05:32:23 am Kostik Belousov wrote: > > > So, I cannot implement overlay of the cdevpriv over the seqaccess data > > > without some additional flag. On the other hand, use of 2 bytes for the > > > f_type is overkill when the range of the types is [1,8]. I divided it > > > to two one-byte fields, and new field is used for filetype-specific > > > flags. > > > > > > http://people.freebsd.org/~kib/misc/fdpriv.4.patch > > > shall give the same size of the struct file while not causing > > > unconditional acquire of the cdevpriv_mtx on the last file close. > > > > > > Jeff, do you agree with the proposed vivisection of the f_type ? I will > > > ask Peter to retest the patch then. > > > > I would rather add the new pointer to struct file and avoid breaking the > > ABI of fstat. That is, I would like this patch to be MFCable, but you > > can't MFC this w/o breaking the ABI of struct file since fstat(1) will be > > reading the full short to get the DTYPE. > > Oh, I thought that fstat uses struct xfile, at least for live systems. > > I considered to introduce new f_type value for devfs files; the > DTYPE_VNODE is not a complete truth due to custom f_ops. But DTYPE_VNODE > is special-cased in enough locations to make this much less preferrable > then another pointer. fstat always uses libkvm and direct access unfortunately. Also, I greatly care about fstat on crash dumps as well. :) -- John Baldwin
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