Re: flushing HFS cache to disk
Re: flushing HFS cache to disk
- Subject: Re: flushing HFS cache to disk
- From: Peter Bierman <email@hidden>
- Date: Wed, 30 Nov 2005 13:53:20 -0800
At 1:35 PM -0800 11/30/05, Dave Yost wrote:
At 12:22 PM -0800 2005-11-30, Shawn Erickson wrote:
On 11/30/05, Dave Yost <email@hidden> wrote:
At 01:32 PM -0800 2005-11-29, Mark Day wrote:
>On Nov 29, 2005, at 12:03 PM, email@hidden wrote:
>
>>>that's what sync(2) does.
>>
>>It doesn't seem to.
>
>Beware that sync(2) is an asynchronous call. It just begins the
flushing of data to all volumes. If you're reading the disk
immediately, the changes may not have been written yet.
Surely there should be a synchronous call one can use.
What happens after that synchronous call returns...? Are you expecting
it to lock out the file system from any other access?
It other words a synchronous call serves no purpose since at any
moment another thread can come along and modify the state of the file
system as long as it is mounted and writable.
Well, it could be specified to guarantee that on return, everything
that was dirty at the time of the call has been flushed to disk,
whether or not anything has been modified during the interval. That
is a purpose that would be served.
Someday, I wish for a file system that is really a true database,
with transactional semantics.
But all the filesystem operations _do_ have transactional semantics.
The issue here is that someone is trying to read from the disk
_behind the back_ of the filesystem. There is NO provision for that
while the filesystem is in use.
-pmb
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