Re: [PATCH] ndctl: add a BTT check utility

[Ross Zwisler <ross.zwisler@linux.intel.com>]

On Fri, Jan 20, 2017 at 12:04:46PM -0800, Dan Williams wrote:
> [ adding Jeff ]
> 
> Some comments on boilerplate / organization items...
> 
> 
> On Thu, Jan 19, 2017 at 7:12 PM, Vishal Verma <vishal.l.verma@intel.com> wrote:
> > Add the check-namespace command to ndctl. This will check the BTT
> > metadata layout for the given namespace, and if requested, correct any
> > errors found. Not all metadata corruption is detectable or fixable.
> >
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
<>
> > +static int btt_read_info(struct btt_chk *bttc, struct btt_sb *btt_sb, __u64 off)
> > +{
> > +       int fd, rc = 0;
> > +       ssize_t size;
> > +
> > +       fd = open(bttc->path, O_RDONLY);
> 
> Let's not open and close the btt device on each call. Open it once at
> the beginning of time and open it O_EXCL so that we prevent the kernel
> trying to claim the device. Let's also use O_DIRECT to bypass the
> block_device page cache.

I thought O_EXCL only mattered if it was used for creation of new files with
O_CREAT?

https://linux.die.net/man/3/open

For us bttc->path is our device in /dev/, so that O_EXCL shouldn't do anything
for us?
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