----- "Bob Montgomery" <bob.montgomery@xxxxxx> wrote: > With respect to character devices: > > Sometime way back in the 2.6ish kernel, the fops field of struct > char_device_struct ceased to be used for anything, and on those > kernels > (like 2.6.18), dev always reports the OPERATIONS field as "(none)": > > crash-4.0-8.10> dev > CHRDEV NAME OPERATIONS > 1 mem (none) > 2 pty (none) > 3 ttyp (none) > 4 /dev/vc/0 (none) > 4 tty (none) > 4 ttyS (none) > 5 /dev/tty (none) > 5 /dev/console (none) > 5 /dev/ptmx (none) > 7 vcs (none) > 10 misc (none) > 13 input (none) > 21 sg (none) > 29 fb (none) > ... > > Then recently (by 2.6.28, anyway), someone noticed that the fops field > was unused and removed it from struct char_device_struct altogether, so > now we get: > > crash-4.0-8.10> dev > > dev: invalid structure member offset: char_device_struct_fops > FILE: dev.c LINE: 221 FUNCTION: dump_chrdevs() > > [/home/bobm/bin/crash-4.0-8.10] error trace: 452e75 => 4cf528 => 4cf957 => 50d8d3 > CHRDEV NAME OPERATIONS > > 50d8d3: OFFSET_verify+168 > 4cf957: dump_chrdevs+1043 > 4cf528: cmd_dev+198 > 452e75: exec_command+306 > > dev: invalid structure member offset: char_device_struct_fops > FILE: dev.c LINE: 221 FUNCTION: dump_chrdevs() > > crash-4.0-8.10> > > The attached patch changes the behavior in both cases to something like > this: > > crash-4.0-8.10fix> dev > CHRDEV NAME OPERATIONS > 1 mem ffffffff8043ee00 <memory_fops> > 2 pty (none) > 3 ttyp (none) > 4 /dev/vc/0 (none) > 4 tty (none) > 4 ttyS (none) > 5 /dev/tty (none) > 5 /dev/console (none) > 5 /dev/ptmx (none) > 7 vcs ffffffff8043ff40 <vcs_fops> > 10 misc ffffffff8043fe40 <misc_fops> > 13 input ffffffff805413c0 <input_fops> > 21 sg (none) > 29 fb ffffffff80531c60 <fb_fops> > > Which is definitely an improvement. > > But wondering about those remaining (none) entries, I found that if I > pursue info through the cdev_map with a series of crash commands like > this: > > crash-4.0-8.10fix> p (*cdev_map.probes[2]).data > $7 = (void *) 0xffff81013a66c408 > crash-4.0-8.10fix> p (*(struct cdev *)0xffff81013a66c408).ops > $8 = (const struct file_operations *) 0xffffffff8043f860 > crash-4.0-8.10fix> sym 0xffffffff8043f860 > ffffffff8043f860 (r) tty_fops > > > crash-4.0-8.10fix> p (*cdev_map.probes[21]).data > $9 = (void *) 0xffff81013acf8d80 > crash-4.0-8.10fix> p (*(struct cdev *)0xffff81013acf8d80).ops > $10 = (const struct file_operations *) 0xffffffff8820ee00 > crash-4.0-8.10fix> sym 0xffffffff8820ee00 > ffffffff8820ee00 (d) sg_fops > > I can come up with believable file_ops values for (most? all?) of the > others. And this leads me to wonder if crash shouldn't be collecting > this info in a similar manner to fill in the other OPERATIONS fields. > But now I'm quite a bit past what I know about how the character device > stuff works. > > > Thanks, > Bob Montgomery > Working at HP Thanks Bob, I appreciate your investigation and patch. I'll take a look (it's been years...), and build upon your patch to have the command dig further when necessary. Dave -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
