Re: 2.6.7-rc2-mm1

[Mikael Pettersson]

Christoph Hellwig writes:
 > > - merged perfctr.  No documentation though :(
 > 
 > +/* tid is the actual task/thread id (népid, stored as ->pid),
 > +   pid/tgid is that 2.6 thread group id crap (stored as ->tgid) */
 > +asmlinkage long sys_vperfctr_open(int tid, int creat)
 > +{
 > +       struct file *filp;
 > +       struct task_struct *tsk;
 > +       struct vperfctr *perfctr;
 > +       int err;
 > +       int fd;
 > +
 > +       if (!vperfctr_fs_init_done())
 > +               return -ENODEV;
 > +       filp = vperfctr_get_filp();
 > +       if (!filp)
 > +               return -ENOMEM;
 > +       err = fd = get_unused_fd();
 > 
 > This really, really screams "I want to be a special file", so the interface
 > still doesn't look okay.  Probably in /proc/pid. 

Been there, done that. open() on /proc/{$pid,self}/perfctr with
or without O_CREAT was the "get initial access" interface for
several years, until the semantics of /proc/$pid (and /proc/self)
completely changed in 2.6.0-test6.

Virtual perfctrs wants something that denotes the real kernel
task, not that process-is-a-group-of-kernel-threads crap.

/Mikael
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