Hi, On Mon, 15 Feb 2010, Jean-Baptiste Lallement wrote: > Initially, I didn't synced the files extracted from the data area but > they were all 0 bytes in case of crash. The situation would be the > same as today.
I understand that but what matters is that they are not 0 bytes if the package is marked as "unpacked", they could end up 0 bytes if the package is marked "half-installed", it would not matter much since the unpack would have to be redone. That's why I why suggesting to call sync() when we switch from half-installed to unpacked instead of calling fsync() individually. > Using sync instead of fsync won't make a big difference I guess, sooner > or later we need do pages need to be flushed to disk and it will have an > effect on system's performance. On the other hand, calling fsync on each > file makes operation atomic and prevent data loss if the crash occurs > during the installation. I understand that. > The call to rename doesn't fsync files nor guarantees which file will be > visible after a crash so we need to call fsync on the directory. I was referring to http://lwn.net/Articles/322823/: "Finally, this patch forces block allocation when one file is renamed on top of another." So it's only true if the rename overwrites a file. But we should not rely on the behaviour of a specific filesystem and we should rather err on the side of caution, I agree and we should not assume this. > > This lead me to believe that it's not the proper place for this code. > > Instead I think (but I would want Guillem's opinion) that it should > > be in process_archive() just after the call to dpkg-deb --control. > > > The idea was to fsync the files as soon as they're extracted. That's why > I've put it there instead of inside dpkg's code. In fact the problem is > more with tar than dpkg. Indeed. > From what I've understood of the behavior of dpkg, when called from > dpkg, the argument `directory' is not null only when we extract the > control files. The parameter is always given AFAIK. > When dpkg-deb is run directly with the extract or vextract command we > want to fsync files. Those commands are not used internally by dpkg AFAIK. So it's not so important as it looks like. > I was unsure where to fsync the control file so I will clearly follow > your advice here. It's my suggestion, but I'm not an expert on the C part of dpkg, if Guillem says something else, please follow his advice. > Thanks for reviewing the code. I'll submit a corrected patch for debian > within a week. Great! Cheers, -- Raphaël Hertzog -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: http://lists.debian.org/20100215084405.gb8...@rivendell
