Messages in this thread | | | Date | Thu, 01 Aug 2002 11:02:43 -0700 | From | Dave Hansen <> | Subject | Re: [RFC] Push BKL into chrdev opens |
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Dave Hansen wrote: > This patch adds the BKL to each character device's open() function. The > BKL will remain in chrdev_open() until the module unload races are > fixed, but this makes it unnecessary there for any other reason.
Greg KH noticed that I'd touched USB, and wondered about the places where get/put_fops were used to make sure the driver gets called directly the next time, instead of going through the subsystem. I don't believe that the BKL is needed in the devices in this case, only in the subsystem itself.
During inode init (init_special_inode) f_op is set to def_chr_fops, which contains chrdev_open First open of char device file: if (f->f_op && f->f_op->open) { error = f->f_op->open(inode,f); } The ->open() call goes to chrdev_open USB is determined to handle the device BKL is grabbed in chrdev_open generic USB ->open() called (usb_open()) driver ->open() is called f_op is replaced with the driver's f_op struct. BKL is released
Subsequent calls: if (f->f_op && f->f_op->open) { error = f->f_op->open(inode,f); } ->open() goes directly to driver. No BKL grabbed after first call. The drivers were only protected during the first call, not during subsequent ones. The addition of the BKL to usb_open() alone duplicates this behavior. Adding BKL to individual devices in cases like this is not required.
The tree is available for pulling from: http://linux-bkl.bkbits.net/linux-2.5-bkl -- Dave Hansen haveblue@us.ibm.com
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