Re: f_op->read seems to be always NULL since Linux 4.1

[Al Viro <viro@ZenIV.linux.org.uk>]

On Sun, Jun 28, 2015 at 08:36:18AM +0200, Andreas Hartmann wrote:
> On Sat, Jun 27, 2015 at 8:10 PM, Richard Weinberger wrote:
> >On Sat, Jun 27, 2015 at 7:32 PM, Andreas Hartmann
> ><andihartmann@01019freenet.de> wrote:
> [...]
> >See __vfs_read().
> >Your module most not rely on such internals.
> 
> Thanks for your hint to the function which exists since 3.19.
> 
> Is there a site out there which lists all relevant changes done for
> each kernel version and the recommendations how to correctly handle
> them?

localhost.  It's in Documentation/filesystems/porting in the kernel
source.  To quote the relevant entry (not far from the end - they
are in chronological order):

[mandatory]
        never call ->read() and ->write() directly; use __vfs_{read,write} or
        wrappers; instead of checking for ->write or ->read being NULL, look for
        FMODE_CAN_{WRITE,READ} in file->f_mode.

Sometimes TFM to R _is_ in the natural place...