Subject: Re: problem with tmpfs and linux emulation?
To: None <firstname.lastname@example.org>
From: Steven M. Bellovin <email@example.com>
Date: 11/09/2005 11:07:23
In message <20051109154841.GA4414@panix.com>, Thor Lancelot Simon writes:
>On Wed, Nov 09, 2005 at 10:40:21AM -0500, Steven M. Bellovin wrote:
>> What, precisely, is the problem? What is there about tmpfs that a
>> application can detect?
>Linux's libc relies on knowledge of the internal structure of directory
>entries rather than manipulating them with the appropriate system calls.
>This causes chaos for those porting filesystems to Linux (e.g. XFS, JFS),
>as well as for those emulating Linux on other systems (e.g. us) or serving
>directories to Linux over network filesystems (because the Linux clients
>don't translate the structure of directories on read(2) either).
>We don't encounter this problem with most local filesystems because the
>in-core directory data structures used by UFS are "close enough". But
>we have a nasty hack to work around it for NFS (which has a performance
>impact, as well as a significant code complexity impact) and we have
>trouble with filesystems that can't trivially provide directory structures
>that look like Linux libc wants them to.
>I have always wondered what Linux does with foreign filesystems like FAT
>and NTFS. I assume that if you try to read a directory, their kernel just
Oh. How, umm, interesting...
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb