Re: Kernel bug: Bad page state: related to generic symlink code and mmap

[Mika Penttilä]

Al Viro wrote:


On Fri, Aug 19, 2005 at 10:16:47PM +0300, Mika Penttilä wrote:
 

Just out of curiosity - what protects even local filesystems against 
concurrent truncate and symlink resolving when using the page cache helpers?
   



How do you get truncate(2) or ftruncate(2) to do something with a symlink?
The former follows links, the latter takes an open file...
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Yes that is right, there is no way to invalidate the symlink inode 
mapping page(s) from user space.


--Mika




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Re: Kernel bug: Bad page state: related to generic symlink code and mmap

[Mika Penttilä]

Al Viro wrote:


On Fri, Aug 19, 2005 at 05:53:32PM +0100, Al Viro wrote:
 


I'm taking NFS helpers to libfs.c and switching ncpfs to them.  IMO that's
better than copying the damn thing and other network filesystems might have
the same needs eventually...
   



[something like this - completely untested]

* stray_page_get_link(inode, filler) - returns ERR_PTR(error) or pointer
to symlink body.  Said symlink body sits in a page at offset equal to
offsetof(page, struct stray_page_link).  filler() is expected to put it
at such offset. Page is cached.

* stray_page_put_link() - ->put_link() suitable for links obtained from
stray_page_get_link().  Unlike the usual pagecache-based variants, this
sucker does _not_ rely on page staying cached.

* nfs and ncpfs switched to the helpers above.

Signed-off-by: Al Viro <[EMAIL PROTECTED]>

 



Just out of curiosity - what protects even local filesystems against 
concurrent truncate and symlink resolving when using the page cache helpers?


--Mika

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