lkml.org 
[lkml]   [2007]   [Jun]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [RFC PATCH 1/4] Union mount documentation.
Date
On Tue, 19 Jun 2007 22:59:51 -0700, Arjan van de Ven wrote:

> user does on FS A:
> mkdir /mnt/A/somedir
> touch /mnt/A/somedir/somefile
>
> and then 2 things happen in parallel
> 1) touch /mnt/B/somefile
> 2) mv /mnt/union/somedir /mnt/union/somefile
>
> since the underlying FS for 2) is FS A... how will this work out locking
> wise? Will the VS lock the union directory only? Or will this operate
> only on the underlying FS? How is dcache consistency guaranteed for
> scenarios like this?

Ok, with Christophs help I guess I know now what the question is :)

touch /mnt/B/somefile is doing a lookup in "B" for "somefile". Therefore it
locks B->i_mutex for that. When it gets a negative dentry it creates the
file.

mv /mnt/union/somedir /mnt/union/somefile is doing a lookup in "union" for
"somefile". Therefore it first locks the i_mutex of the topmost directory
in the union of "/mnt/union" (which happens to be "B"). When it gets a
negative dentry it than follows the union down to the next layer (with the
topmost directory still locked). Lookup is repeated until a filled dentry
is found or the topmost dentry negative dentry is used as a target for the
move. Thats it.

Did that answer your question?

Cheers,
Jan

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-20 15:09    [W:0.077 / U:3.552 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site