Messages in this thread | | | Date | Sat, 12 Mar 2011 00:45:47 +0100 (CET) | Subject | Re: [PATCH v3] introduce sys_syncfs to sync a single file system | From | "Indan Zupancic" <> |
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On Fri, March 11, 2011 12:55, Arnd Bergmann wrote: > On Friday 11 March 2011, Indan Zupancic wrote: >> > http://marc.info/?l=linux-fsdevel&m=127970513829285&w=2 >> >> The patch there seems much more reasonable than introducing a whole >> new systemcall just for 20 lines of kernel code. New system calls are >> added too easily nowadays. > > The only problem with adding new system calls is that we are stuck > with the interface until the end of time, so we must be sure not > to get it wrong. The same thing is true for any other interface > such as ioctl or extensions to existing system calls. People usually > get away with adding new ioctls more easily because it is less > obvious when they are added.
Agreed.
I'm not sure this feature is important enough to add. I can't really think of a regular use case where this would be useful, generally it's transparent on which mount files are. Add symlinks, and you give users a lot of rope. Any user has to make sure that all the files they want to sync are on the same file system.
About the arguments against sync(2):
> - On machines with many mounts, it is not at all uncommon for some of > them to hang (e.g. unresponsive NFS server). sync(2) will get stuck on > those and may never get to the one you do care about (e.g., /).
It would be better to fix NFS, or mount it with the fsc option (assuming a sync will write to the local cache instead of hanging forever then).
> - Some applications write lots of data to the file system and then > want to make sure it is flushed to disk. Calling fsync(2) on each > file introduces unnecessary ordering constraints that result in a large > amount of sub-optimal writeback/flush/commit behavior by the file > system.
You can use sync_file_range() on those files to schedule the writes and then do the fsync(2) as usual (both on files and dirs).
If there still is a good reason to implement this, please don't add it as a new system call, but add it to sync_file_range(), as that seems the best place for odd file synchronisation operations.
Greetings,
Indan
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