From: Al Viro <viro@zeniv.linux.org.uk>
To: "\"Kai Mäkisara (Kolumbus)\"" <kai.makisara@kolumbus.fi>
Cc: Christoph Hellwig <hch@lst.de>,
linux-fsdevel@vger.kernel.org,
Octavian Purdila <octavian.purdila@intel.com>,
Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-scsi@vger.kernel.org
Subject: Re: [RFC] Re: broken userland ABI in configfs binary attributes
Date: Mon, 26 Aug 2019 20:32:10 +0100 [thread overview]
Message-ID: <20190826193210.GP1131@ZenIV.linux.org.uk> (raw)
In-Reply-To: <B35B5EA9-939C-49F5-BF65-491D70BCA8D4@kolumbus.fi>
On Mon, Aug 26, 2019 at 09:34:37PM +0300, "Kai Mäkisara (Kolumbus)" wrote:
>
>
> > On 26 Aug 2019, at 19.29, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > On Mon, Aug 26, 2019 at 03:48:38AM +0100, Al Viro wrote:
> >
> >> We might be able to paper over that mess by doing what /dev/st does -
> >> checking that file_count(file) == 1 in ->flush() instance and doing commit
> >> there in such case. It's not entirely reliable, though, and it's definitely
> >> not something I'd like to see spreading.
> >
> > This "not entirely reliable" turns out to be an understatement.
> > If you have /proc/*/fdinfo/* being read from at the time of final close(2),
> > you'll get file_count(file) > 1 the last time ->flush() is called. In other
> > words, we'd get the data not committed at all.
> >
> ...
> > PS: just dropping the check in st_flush() is probably a bad idea -
> > as it is, it can't overlap with st_write() and after such change it
> > will…
> Yes, don’t just drop it. The tape semantics require that a file mark is written when the last opener closes this sequential device. This is why the check is there. Of course, it is good if someone finds a better solution for this.
D'oh... OK, that settles it; exclusion with st_write() would've been
painful, but playing with the next st_write() on the same struct file
rewinding the damn thing to overwrite what st_flush() had spewed is
an obvious no-go.
next prev parent reply other threads:[~2019-08-26 19:32 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-26 2:48 broken userland ABI in configfs binary attributes Al Viro
2019-08-26 16:29 ` [RFC] " Al Viro
2019-08-26 18:20 ` Matthew Wilcox
2019-08-26 19:28 ` Al Viro
2019-08-27 8:51 ` Miklos Szeredi
2019-08-27 11:58 ` Al Viro
2019-08-27 12:21 ` Miklos Szeredi
2019-08-27 12:53 ` Al Viro
2019-08-31 8:32 ` Christoph Hellwig
2019-08-31 13:35 ` Al Viro
2019-08-31 14:44 ` Christoph Hellwig
2019-08-31 15:58 ` Al Viro
2019-08-26 18:34 ` "Kai Mäkisara (Kolumbus)"
2019-08-26 19:32 ` Al Viro [this message]
2019-08-27 15:01 ` Boaz Harrosh
2019-08-27 17:27 ` Al Viro
2019-08-27 17:59 ` Boaz Harrosh
2019-08-29 22:22 ` Al Viro
2019-08-29 23:32 ` Al Viro
2019-08-30 4:10 ` Dave Chinner
2019-08-30 4:44 ` Al Viro
2019-08-31 8:28 ` Christoph Hellwig
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