Re: clone_cleanup() doesn't

On Fri, 14 Aug 2009, Andrew Gallatin wrote:

> I've been porting a closed-source driver to FreeBSD 8 from FreeBSD 5/6/7. It 
> use the dev_clone() eventhandler to mimic linux-like open semantics (for 
> linux binary compat).

No particular experience with unloading cloning stuff, but have you noticed 
that in 8.x we now have per-file descriptor device state?  This is often the 
semantics people actually want, rather than cloning.  See 
devfs_set_cdevpriv(9) for details -- there are several synthetic devices in 
the tree that use it now (although some of them do too much error-checking, 
and should assert rather than return errors, I think).

Robert N M Watson
Computer Laboratory
University of Cambridge

>
> From the eventhandler, I do:
>
>  fake_unit = -1;
>  i = clone_create(&mx_clones, &mx_cdevsw, &fake_unit, cdev, 0);
>
>  if (i) {
>    /* need to allocate a new /dev/mx_fake.%d device node */
>    *cdev = make_dev(&mx_cdevsw, unit2minor(fake_unit),
> 		    UID_ROOT, GID_WHEEL,
> 		    mode, "mx_fake.%d", fake_unit);
>  }
>
> This has worked fine from 5.x through 7.x,
> but in 8.x, the /dev/mx_fake.* devices persist after
> unload.  If anything attempts to access them, the machine
> falls over (trace appended).
>
> I'm assuming these files are lingering because clone_cleanup()
> (called at device detach) is not cleaning up these lingering
> device nodes.  I've tried writing a dtrace script to trace
> clone_cleanup.  But since that happens from device detach,
> dtrace doesn't work (blocks driver unload).  I've also tried
> setting a breakpoint in ddb(), but the breakpoint seems to
> be ignored (other breakpoints work fine, which is odd).
>
> What changed between 7.x and 8 with respect to device cloning?
>
> BTW, is there any easier option now in 8.x?
>
> Thanks,
>
> Drew
>
> Fatal trap 12: page fault while in kernel mode
> cpuid = 0; apic id = 00
> fault virtual address   = 0xffffffff81528a64
> fault code              = supervisor read data, page not present
> instruction pointer     = 0x20:0xffffffff8052f009
> stack pointer           = 0x28:0xffffff8018a75730
> frame pointer           = 0x28:0xffffff8018a757a0
> code segment            = base 0x0, limit 0xfffff, type 0x1b
>                        = DPL 0, pres 1, long 1, def32 0, gran 1
> processor eflags        = interrupt enabled, resume, IOPL = 0
> current process         = 18087 (cat)
> [thread pid 18087 tid 100061 ]
> Stopped at      devfs_open+0x69:        testb   $0x4,0x4(%rax)
> db> bt
> Tracing pid 18087 tid 100061 td 0xffffff000188bab0
> devfs_open() at devfs_open+0x69
> VOP_OPEN_APV() at VOP_OPEN_APV+0x44
> vn_open_cred() at vn_open_cred+0x2f4
> kern_openat() at kern_openat+0x179
> syscall() at syscall+0x28f
> Xfast_syscall() at Xfast_syscall+0xd0
> --- syscall (5, FreeBSD ELF64, open), rip = 0x8007272ac, rsp = 
> 0x7fffffffe0d8, rbp = 0 ---
> db>
> Tracing pid 18087 tid 100061 td 0xffffff000188bab0
> devfs_open() at devfs_open+0x69
> VOP_OPEN_APV() at VOP_OPEN_APV+0x44
> vn_open_cred() at vn_open_cred+0x2f4
> kern_openat() at kern_openat+0x179
> syscall() at syscall+0x28f
> Xfast_syscall() at Xfast_syscall+0xd0
> --- syscall (5, FreeBSD ELF64, open), rip = 0x8007272ac, rsp = 
> 0x7fffffffe0d8, rbp = 0 ---
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