Date: Thu, 18 Jul 2002 14:42:20 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: John Baldwin <jhb@FreeBSD.ORG>, current@FreeBSD.ORG Subject: Re: Questions about kern_descrip.c Message-ID: <3D37363C.3DF4C315@mindspring.com> References: <XFMail.20020718134618.jhb@FreeBSD.org> <200207181840.g6IIe25G019269@apollo.backplane.com>
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Matthew Dillon wrote: > The issue with dup2() was a race against open() or close() > I believe, where dup2() could potentially dup into a > descriptor that open() was about to use. Unfortunately, it > does appear that dup() has the same issue. > > fdalloc() does not reserve the descriptor number it > returns, it simply finds a free slot and says 'this > index is a free slot'. Even in the latest -current, > fdalloc() releases the fdp lock when it goes to > MALLOC so the race appears to still be present. The correct way to deal with this is to make the descriptor slot allocation happen at a higher layer, and pass the address of it in as an agrument to the code. This will incidently let you pass in a static or other non-FD table associated descriptor in place to all these calls, which will have the effect of permitting you to do "descriptor" based file I/O from kernel space much, much easier. If the work would be accepted as a delta against -stable, I would be willing to do it, since I need kernel file I/O, and the problem hasn't been solving itself for about six years now. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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