git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / mirror / code / Atom feed
From: Chris Torek <chris.torek@gmail.com>
To: "René Scharfe" <l.s.r@web.de>
Cc: Git Mailing List <git@vger.kernel.org>,
	Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH] upload-pack: use buffered I/O to talk to rev-list
Date: Mon, 3 Aug 2020 08:54:55 -0700	[thread overview]
Message-ID: <CAPx1Gvd7rULr-Z-mLDc2FCxyoepdMhK2t=j23-mr_6pvvHWynw@mail.gmail.com> (raw)
In-Reply-To: <87c4ab84-8db5-bd62-af66-fd88f788827b@web.de>

On Mon, Aug 3, 2020 at 7:00 AM René Scharfe <l.s.r@web.de> wrote:
>
> Am 02.08.20 um 18:03 schrieb Chris Torek:
> > The fclose() call doesn't necessarily check ferror().  (The
> > FreeBSD stdio in particular definitely does not.)
>
> Thanks, didn't know that.  That's awful.  So the sentence "The fclose()
> and fdclose() functions may also fail and set errno for any of the
> errors specified for fflush(3)." from the FreeBSD manpage for fclose(3)
> actually means that while it will flush, it is free to ignore any
> flush errors?
>
> Or do you mean that fflush() can succeed on a stream that has its error
> indicator set?

The latter.  You have to get particularly (un?)lucky here: say the
buffer size is n, and the *last* write operation (fprintf, whatever)
filled the buffer mod n and called fflush internally and that failed.
Then at the time you call fclose() the buffer is empty.  There is
nothing to flush, so we just get the result of the system's close()
call.

> In any case, we'd then better add a function that flushes the buffer,
> closes the stream and reports errors in its return code and errno --
> i.e. a sane fclose().

Unfortunately the global-variable nature of errno means it may be
clobbered by the time you inspect it here, again with the same sort
of issue above.  It might be nice if C's error conventions were more
like Go's, and stdio retained an earlier error, but this stuff all dates
back to 16-bit "int" and 512-byte buffers and no room for nice stuff. :-)

Chris

  reply	other threads:[~2020-08-03 15:55 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-02 14:38 René Scharfe
2020-08-02 16:03 ` Chris Torek
2020-08-03 14:00   ` René Scharfe
2020-08-03 15:54     ` Chris Torek [this message]
2020-08-03 18:15   ` Johannes Sixt
2020-08-12 16:52 ` [PATCH v2] " René Scharfe
2020-08-13  5:17   ` Christian Couder
2020-08-13  5:57     ` René Scharfe
2020-08-13  9:01       ` Jeff King

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAPx1Gvd7rULr-Z-mLDc2FCxyoepdMhK2t=j23-mr_6pvvHWynw@mail.gmail.com' \
    --to=chris.torek@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=l.s.r@web.de \
    --subject='Re: [PATCH] upload-pack: use buffered I/O to talk to rev-list' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Code repositories for project(s) associated with this inbox:

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).