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Re: Patch to retrieve send rights for shared memory objects

From: Roland McGrath
Subject: Re: Patch to retrieve send rights for shared memory objects
Date: Mon, 28 Feb 2005 14:35:14 -0800 (PST)

> Ok.  Should we change diskfs_get_filemap to accept a flag that says we do
> not want to create the memory object if it doesn't exist already?  That
> seems to be an important optimization to me if we call it in io_stat.

diskfs shouldn't be assuming anything about the filesystem's memory object
ports and how to guess how many mappers there might be and so forth.
Probably the easiest thing to do is just have the filesystem set these
st_mode bits directly itself in dn_stat.  It knows when it passes out the
memory object in the first place, so it can clear S_IMMAP0 then.  If it's
necessary to do an active check at stat time to figure out how many mappers
there might be, then this can be a new callback made by diskfs_S_io_stat.
e.g., diskfs_modify_stat called just before unlocking the node.
The library can provide a no-op default definition of the function so that
old filesystems keep linking if they haven't been enhanced to produce the
new bits.


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