Re: kern/164674: vsprintf/vswprintf return error (EOF) on succes
The following reply was made to PR kern/164674; it has been noted by GNATS.
From: Matthew Story <matthewstory@gmail.com>
To: freebsd-gnats-submit@freebsd.org, freebsd-standards@freebsd.org
Cc:
Subject: Re: kern/164674: vsprintf/vswprintf return error (EOF) on success if
__SERR flag is already set on file
Date: Thu, 16 Feb 2012 10:55:11 -0500
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On Tue, Jan 31, 2012 at 6:06 PM, Matthew Story <matthewstory@gmail.com>wrote:
>
> >Number: 164674
> >Category: kern
> >Synopsis: vfprintf/vfwprintf return error (EOF) on success if
> __SERR flag is already set on file
>
Apologies for cross-posting, but I think that standards might be a more
appropriate responsible party for this than -bugs or kern. See description
for more info, but the basic issue is that C99 and C11 stipulate that
fprintf should return -1 "if an output or encoding error occurred."
Currently, printf is encoding and outputting successfully (on line or fully
buffered FILEs), but returning -1 if the FILE has an error. The C99/C11
specifications make no mention of FILE state in fprintf return conditions,
so this functionality seems to not conform to the specification, attached
patch resolves that issue.
> >Confidential: no
> >Severity: non-critical
> >Priority: low
> >Responsible: freebsd-bugs
> >State: open
> [...snip]
> >Description:
> The printf family of functions behaves unpredictably if the file passed to
> the function has the __SERR flag set in _flags. The one consistency across
> all of the cases detailed below is that regardless of the number of bytes
> written to the file, and the success/failure of that operation, the printf
> functions (printf, fprintf, wprintf, fwprintf) will always return -1 (EOF).
>
> * For the case of an unbuffered file, the operation currently fails
> transmitting no bytes, and returns -1.
> * For the case of a buffered file, the operation transmits all bytes and
> the function returns -1.
>
> The problem is that the behavior here is inconsistent, and should not be.
> The question is wether all should be made to fail consistently and
> transmit no bytes if __SERR is set on _flags, or if failure should be
> determined based on the success of byte transmission, discounting file
> state.
>
> Per the ISO/IEC 9899:201x (C11) Section 7.21.6.1, 14:
>
> The fprintf function returns the number of characters transmitted, or a
> negative value if an output or encoding error occurred.
>
> My reading of this specification is that success should be determined
> based on byte-transmission, and should not factor-in file state. In
> addition to the ISO standard, the glibc implementation will reliably
> succeed with any error flag set if bytes are successfully transmitted
> (although it will transmit partial messages prior to successful conversion,
> which is unfortunate).
>
> The attached patch makes the operation on buffered and unbuffered files
> consistent across the affected printf/wprintf functions, determines
> success/failure based on successful byte-transmission alone, and preserves
> _flags state for __SERR as passed in.
>
> [...snip]
--
regards,
matt
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On Tue, Jan 31, 2012 at 6:06 PM, Matthew Story <span dir=3D"ltr"><<a hre=
f=3D"mailto:matthewstory@gmail.com" target=3D"_blank">matthewstory@gmail.co=
m</a>></span> wrote:<br><div class=3D"gmail_quote"><blockquote class=3D"=
gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-=
left:1ex">
<br>
>Number: =A0 =A0 =A0 =A0 164674<br>
>Category: =A0 =A0 =A0 kern<br>
>Synopsis: =A0 =A0 =A0 vfprintf/vfwprintf return error (EOF) on success =
if __SERR flag is already set on file<br></blockquote><div><br></div><div>A=
pologies for cross-posting, but I think that standards might be a more appr=
opriate responsible party for this than -bugs or kern. =A0See description f=
or more info, but the basic issue is that C99 and C11 stipulate that fprint=
f should return -1 "if an output or encoding error occurred." Cur=
rently, printf is encoding and outputting successfully (on line or fully bu=
ffered FILEs), but returning -1 if the FILE has an error. =A0The C99/C11 sp=
ecifications make no mention of FILE state in fprintf return conditions, so=
this functionality seems to not conform to the specification, attached pat=
ch resolves that issue.</div>
<div>=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;=
border-left:1px #ccc solid;padding-left:1ex">
>Confidential: =A0 no<br>
>Severity: =A0 =A0 =A0 non-critical<br>
>Priority: =A0 =A0 =A0 low<br>
>Responsible: =A0 =A0freebsd-bugs<br>
>State: =A0 =A0 =A0 =A0 =A0open<br>[...snip]<br>
>Description:<br>
The printf family of functions behaves unpredictably if the file passed to =
the function has the __SERR flag set in _flags. =A0The one consistency acro=
ss all of the cases detailed below is that regardless of the number of byte=
s written to the file, and the success/failure of that operation, the print=
f functions (printf, fprintf, wprintf, fwprintf) will always return -1 (EOF=
).<br>
<br>
=A0* For the case of an unbuffered file, =A0the operation currently fails t=
ransmitting no bytes, and returns -1.<br>
=A0* For the case of a buffered file, the operation transmits all bytes and=
the function returns -1.<br>
<br>
The problem is that the behavior here is inconsistent, and should not be. =
=A0 The question is wether all should be made to fail consistently and tran=
smit no bytes if __SERR is set on _flags, or if failure should be determine=
d based on the success of byte transmission, discounting file state.<br>
<br>
Per the ISO/IEC 9899:201x (C11) Section 7.21.6.1, 14:<br>
<br>
The fprintf function returns the number of characters transmitted, or a neg=
ative value if an output or encoding error occurred.<br>
<br>
My reading of this specification is that success should be determined based=
on byte-transmission, and should not factor-in file state. =A0In addition =
to the ISO standard, the glibc implementation will reliably succeed with an=
y error flag set if bytes are successfully transmitted (although it will tr=
ansmit partial messages prior to successful conversion, which is unfortunat=
e).<br>
<br>
The attached patch makes the operation on buffered and unbuffered files con=
sistent across the affected printf/wprintf functions, determines success/fa=
ilure based on successful byte-transmission alone, and preserves _flags sta=
te for __SERR as passed in.<br>
<br>[...snip]</blockquote></div><div><br></div>-- <br>regards,<br>matt<br>
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