Re: splice() and file offsets

[Michael Kerrisk]

Jens,

> > Yes, I understand what the code is doing, but *why* do 
> > things this way?  (To put things another way: why not *always 
> > have splice() update the file offset?)  I realise there may be
> > some good reason for this, and if there is, it will go into the
> > man page!
> 
> The good reason is why update the current position? I just told the
> kernel to ignore the current position and use the given offset, why
> would I bother updating the current position? The whole point of
> providing an offset is to ignore the current position.
> 
> I must say I cannot understand why you are confused or find this
> illogical, it makes perfect sense to me.

Yes, now it's clear to me too.

[...]

> > No!  It does not!  See the sendfile.2 man page: "sendfile() 
> > does not modify the current file offset of in_fd."  
> 
> I didn't read the man page, I read the source. And it clearly updates
> the file offset, in fact the actual sendfile portion is just a supplied
> actor to the generic page cache read functions.

Doh!  I took what I "knew", re-read the sendfile.2 manual page to 
check, misread the source, and then wrote an inadequate 
test program :-{.  (The sendfile manual page is now fixed.)

> If you don't believe me, read the source and do another test app.
> splice() behaves identically, as previously stated.

Now I believe you; sorry to have wasted your time...

Cheers,

Michael
-- 
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7 

Want to help with man page maintenance?  
Grab the latest tarball at
ftp://ftp.win.tue.nl/pub/linux-local/manpages/, 
read the HOWTOHELP file and grep the source 
files for 'FIXME'.
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