Subject: Re: UBC problems
To: Chuck Silvers <firstname.lastname@example.org>
From: Steven M. Bellovin <email@example.com>
Date: 01/15/2005 11:27:11
In message <20050115154734.GA29402@spathi.chuq.com>, Chuck Silvers writes:
>On Sat, Jan 15, 2005 at 10:36:39AM -0500, Steven M. Bellovin wrote:
>> In message <20050115151907.GA9021@spathi.chuq.com>, Chuck Silvers writes:
>> >> -I now believe that the best way to deal with this would be to
>> >> have UBC reads just return zero filled pages if the file is
>> >> not backed with real data, and let upper layers (above the
>> >> trap handler) check whether the read is legal. Just commenting
>> >> out the range check in genfs_getpages() isn't enough,
>> >> unfortunately. That's a pretty complex matter...
>> >creating pages for offsets past EOF is to be avoided in general, since
>> >it's pretty nonsensical. I checked in a different fix for this issue,
>> >update uvm_bio.c.
>> I don't understand -- are you trying to bar files with holes in them?
>> That's been part of Unix since the beginning.
>no, seeking past EOF and write()ing still works. we just don't want to
>allow read operations for offsets past EOF.
That sounds reasonable, though I'd like to check against classical Unix
semantics or POSIX.
--Prof. Steven M. Bellovin, http://www.cs.columbia.edu/~smb