Re: CD writing in future Linux (stirring up a hornets' nest)

[Kyle Moffett]

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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