directio, O_DIRECT, "mount -o sync", O_SYNC, O_DSYNC and all that
directio, O_DIRECT, "mount -o sync", O_SYNC, O_DSYNC and all that
- Subject: directio, O_DIRECT, "mount -o sync", O_SYNC, O_DSYNC and all that
- From: Reto Kramer <email@hidden>
- Date: Wed, 17 Aug 2005 16:47:01 -0700
I'm looking for a way to (1) enable direct IO on OS X (10.4) and (2)
a way to write w/o updating metadata (i.e. last access time). All in
the context of the ever popular tx log file use case.
- are there plans to support O_DIRECT, or mount -o forcedirectio
(disable cache)?
- are there plans to support the O_DSYNC open flag (avoid some
metadata update, i.e. last access time)?
To help me understand what is available (what I found at least) in
10.4, I appreciate your help with the following 3 questions:
(a) is the sync mount option equivalent to the directio flag, I can
e.g. get on Solaris?, or
(b) if I open a file with O_SYNC (in fcntl.h but not "man 2 open"
page) is this the same as writing to a file on a FS that I mounted
with "mount -o sync" ?
(c) is writing (write system call) to a "-o sync" mounted FS (HFS+)
equivalent to fsync'ing the fd (I only care about a single tx log
file), except that I save a system call? I.e. can I be assured that
(module the fcntl F_FULLSYNC call) the data is flushed to disk if I
write to a "-o sync" HFS, or "D_SYNC" opened file?
Thanks,
- Reto
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