[PATCH] Never cache offset when the stream handle is not active (BZ #16680)

[Siddhesh Poyarekar]

Resending, this is hopefully in plain text now.

Siddhesh

On 11/03/2014, Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com> wrote:
> On Tuesday, 11 March 2014, Rich Felker <dalias@aerifal.cx> wrote:
>
>> On Tue, Mar 11, 2014 at 06:09:35AM +0530, Siddhesh Poyarekar wrote:
>> > On Mon, Mar 10, 2014 at 02:34:59PM -0400, Rich Felker wrote:
>> > > Caching the offset is valid when writing in append mode. The one case
>> > > that's special for append mode is that, even once the handle is
>> > > active, you can't save the resulting offset at the time of
>> > > seek/rewind
>> > > and use it for ftell during subsequent writing. This is because the
>> > > (first) write after seeking could change the current offset. One easy
>> > > way to deal with this is to treat seek/rewind as deactivating the
>> > > handle when the stream is in append mode, but more fine-grained
>> > > solutions are possible too.
>> >
>> > Treating seek/rewind as deactivating the handle won't help for append
>> > mode because we want to simulate the file position as being the end of
>> > file regardless of the file position when the handle is inactive, but
>>
>> Why do you want to do this? It's wrong. If the handle is inactive, the
>
> only way you can get the position is by calling lseek(fd,0,SEEK_CUR).
>
> This is because operations on another handle could have changed the
>> position without stdio's knowledge.
>>
>
> Because that would give an inconsistent result. Initial position for append
> mode files is implementation defined and glibc has set it as end of file in
> the past. Changing that would be a breakage, wouldn't it?
>
> Siddhesh
>
>
> --
> http://siddhesh.in
>


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