Re: f_ops flag to speed up compatible ioctls in linux kernel

[Michael S. Tsirkin]

Quoting Lee Revell (rlrevell@xxxxxxxxxxx) "Re: f_ops flag to speed up compatible ioctls in linux kernel":
> By adding a new ioctl you are adding a new use of the BKL.  It has been
> suggested on dri-devel that this should be fixed.  Is this even
> possible?
> 
> Lee

I dont know - can the lock be released before the call to
filp->f_op->ioctl ?

I assume the reason its there is for legacy code - existing ioctls
may be assuming the BKL is taken, but maybe there could be another
flag in f_ops to let sys_ioctl release the lock before doing the call ...

Like this - would that be safe?


--- linux-2.6.8.1/fs/ioctl.c	2004-08-14 13:54:51.000000000 +0300
+++ linux-2.6.8.1-built/fs/ioctl.c	2004-09-01 11:14:59.944417160 +0300
@@ -126,6 +126,14 @@
 			error = -ENOTTY;
 			if (S_ISREG(filp->f_dentry->d_inode->i_mode))
 				error = file_ioctl(filp, cmd, arg);
+			else if (filp->f_op && filp->f_op->ioctl &&
+				(filp->f_op->fops_flags & FOPS_IOCTL_NOLOCK)) {
+			{
+				unlock_kernel();
+				error = filp->f_op->ioctl(filp->f_dentry->d_inode, filp, cmd, arg);
+				goto out;
+
+			}
 			else if (filp->f_op && filp->f_op->ioctl)
 				error = filp->f_op->ioctl(filp->f_dentry->d_inode, filp, cmd, arg);
 	}

-
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