Subject: Re: problem with tmpfs and linux emulation?
To: Matt Thomas <email@example.com>
From: Steven M. Bellovin <firstname.lastname@example.org>
Date: 11/12/2005 13:59:26
In message <43763B07.email@example.com>, Matt Thomas writes:
>Steven M. Bellovin wrote:
>> In message <437637E2.firstname.lastname@example.org>, Matt Thomas writes:
>>>Bill Studenmund wrote:
>>>I don't see the problem. Instead of using sys_read, linux would have its
>>>linux_sys_read. It would look up the fd, see if it's a DTYPE_VNODE, and if
>>>check to see if it's a directory. It's only a problem is you are relying on
>>>he standard sys_read routine.
>> Presumably, though, the behavior of linux_sys_read would have to depend
>> on the underlying file system type -- it does the right thing for, say,
>> ffs and ext2fs, but not for tmpfs.
>But it only work by "accident", not intention. This method should be used for
>all filesystems, not just tmpfs. It's a bit more inefficient, but more correc
I agree, with one caveat: would the linux_sys_read layer have enough
information to fix things, regardless of the semantics of the
underlying file system? If not, we have a lot of file systems to fix
to pass the proper information up to the emulation layer.
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb