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havp on linux mandatory lock is mandatory? http://havp.hege.li/forum/viewtopic.php?f=3&t=417 |
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Author: | afer [ 16 Mar 2009 13:49 ] |
Post subject: | havp on linux mandatory lock is mandatory? |
Hi and thx for havp. I'm running Linux, Ubuntu 8.04, and I think that the following could apply to my kernel: http://www.mjmwired.net/kernel/Document ... ocking.txt : Mandatory File Locking For The Linux Operating System 2 3 Andy Walker <andy[AT]lysaker.kvaerner[DOT]no> 4 5 15 April 1996 6 (Updated September 2007) 7 8 0. Why you should avoid mandatory locking 9 ----------------------------------------- 10 11 The Linux implementation is prey to a number of difficult-to-fix race 12 conditions which in practice make it not dependable: 13 14 - The write system call checks for a mandatory lock only once 15 at its start. It is therefore possible for a lock request to 16 be granted after this check but before the data is modified. 17 A process may then see file data change even while a mandatory 18 lock was held. 19 - Similarly, an exclusive lock may be granted on a file after 20 the kernel has decided to proceed with a read, but before the 21 read has actually completed, and the reading process may see 22 the file data in a state which should not have been visible 23 to it. 24 - Similar races make the claimed mutual exclusion between lock 25 and mmap similarly unreliable. Now I have only one disk partition on my proxy server running havp with clamav and squid, so I'd like to know why I should use mandatory lock for havp. If I don't use it what will be the consequences? Best regards, Andrea Ferraris |
Author: | afer [ 17 Mar 2009 14:02 ] |
Post subject: | Re: is havp on linux mandatory lock mandatory? |
Maybe is only the INSTALL doc that is not up to date? I noticed that the installation created such device: /var/lib/havp/havp.loop on /var/spool/havp type ext3 (rw,mand,loop=/dev/loop0) and I found there some dir that seems temporary. Is it right? I don't have to care about mounting with mandatory lock my root file system? Regards |
Author: | hege [ 17 Mar 2009 15:29 ] |
Post subject: | Re: havp on linux mandatory lock is mandatory? |
HAVP installation does not create anything. You are using distribution package, which may do it's own things. Without locking, files cannot be scanned as they are received. If your scansize is 5MB for example, server needs to wait until it's fully received, scan it and then only start sending to client. It's not mandatory if you don't mind some delays for large files. |
Author: | afer [ 17 Mar 2009 16:47 ] |
Post subject: | Re: havp on linux mandatory lock is mandatory? |
thx |
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