On Tue, Jul 14, 2020 at 09:04:21PM +0200, Christoph Hellwig wrote:

-		ssize_t rv = ksys_write(fd, p, count);
+		ssize_t rv = kernel_write(file, p, count, &file->f_pos);

No.  Sure, that'll work for ramfs with nobody else playing with those.
However, this is the wrong way to do such things; do *NOT* pass the
address of file->f_pos to anything.  The few places that still do that
are wrong.

As a general rule, ->read() and ->write() instances should never be
given &file->f_pos.  Address of a local variable - sure, no problem.
Copy it back into ->f_pos when they are done?  Also fine.  But not
this,

Keep that offset in a variable (static in file, argument of xwrite(),
whatever).