On Sat, Dec 03, 2011 at 09:36:56PM +0100, Corinna Vinschen wrote: >On Dec 2 13:04, Eric Blake wrote: >> On 12/02/2011 11:50 AM, Jon Clugston wrote: >> > While this loop is running, the timestamp on "x.log" doesn't change >> > (whereas on Linux it changes every 10 seconds). It sure looks to me >> > that Windows just doesn't bother updating the file timestamp while it >> > is open. I don't know if this update is required by POSIX - I would >> > doubt that it is. >> >> POSIX requires that any write() to an open file mark it for update; the >> update doesn't have to occur right away (so you can batch up several >> writes, but only change the mtime metadata once at the end of the >> batch), but it DOES require that stat() and several similar functions >> flush all marked updates prior to exposing timestamps to the user. So >> yes, Windows is violating POSIX, and I have no idea whether cygwin can >> work around it. > >You can change all file operations to use FILE_WRITE_THROUGH and >FILE_NO_INTERMEDIATE_BUFFERING. Downside: No caching. All file >operations must be sector aligned. Degraded system performance. >Broken when a process has only write permissions. > >Alternatively, change write(2) so that every WriteFile call is >accompanied by a FlushFileBuffers call. Downside: Extremly degraded >write performance. > >Alternatively: Lie. That's how SUA does it. It has a background >service running which (among other things) keeps track of write >operations of SUA applications. If a SUA application calls write(2) >the write timestamp is kept up to date internally, while the metadata >on disk is still lagging in Windows style. A SUA application calling >stat(2) gets a POSIX compatible timestamp. Non-SUA apps continue to >show the "wrong" timestamp. If non-SUA apps write to a file, SUA apps >also show the Windows timestamp. Cygwin could do the same. Downside: >We don't have a mandatory background service running. Quite a hoop to >jump through to implement a usually non-critical POSIX requirement.
Since I believe that this has come up before is anyone willing to provide a FAQ entry that we can point to in the future? cgf -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
