Messages in this thread | | | From | Kyle Moffett <> | Subject | Re: CD writing in future Linux (stirring up a hornets' nest) | Date | Sun, 5 Feb 2006 12:50:50 -0500 |
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On Feb 05, 2006, at 11:15, Phillip Susi wrote: > Jan Engelhardt wrote: >> I would say we all forgot to RTFM. Because O_EXCL does nothing >> *unless* O_CREAT is specified, which probably *is not* specified >> in cdrecord or hal. There is no reason to have hal or cdrecord >> create a device node - which you can't do with open() anyway. > > I think you are misinterpreting the man page, because it isn't > worded very clearly. It should not even mention O_CREAT because it > has nothing to do with O_EXCL; it is just repeating the semantics > of O_CREAT ( if the file already exists, the call fails ) which > would of course, apply if you do use O_CREAT in conjunction with > any other flag including O_EXCL. It does not say that you must use > O_EXCL with O_CREAT. The rest of the description talks about using > lockfiles as an alternative to ensure exclusive access to the file > on NFS where O_EXCL is broken. The intent of O_EXCL is clearly to > provide the caller with exclusive access to the file.
You don't have this right either. The way open() works:
If you specify O_CREAT (and not O_EXCL), it will create the file if it does not exist, and open the existing file otherwise.
If you specify O_EXCL (and not O_CREAT), it is implementation defined what will happen (in the Linux case, this opens a block device for exclusive access).
If you specify O_CREAT|O_EXCL, it will atomically create the file if it does not exist, otherwise it will return the error -EEXIST.
Cheers, Kyle Moffett
-- Q: Why do programmers confuse Halloween and Christmas? A: Because OCT 31 == DEC 25.
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