Messages in this thread | | | Date | Mon, 5 Jul 1999 16:06:44 -0600 (MDT) | From | Jason Gunthorpe <> | Subject | Re: Loop Devices over NFS don't work? |
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On Mon, 5 Jul 1999, Alan Cox wrote:
> > Oh, in that case shouldn't losetup fail with an error? > > > > Also, is it really necessary to have bmap to do loop devices? Couldn't > > some sort of alternate mechanism be used? > > You could fall back to read/write in theory. There is an interesting project > for you 8)
Hrm, I have tried a few things, and I am having poor luck making read work in kernel space. I am using a call like this:
lo->lo_dentry->d_inode->i_op-> default_file_ops->read(lo->lo_backing_file,dest_addr,len, &lo->lo_backing_file->f_pos));
Which I belive goes over to mm/filemap.c:generic_file_read which then seems to return efault because access_ok says that it cannot write to dest_addr (which should be within a buffer head, I think)
I'm going to guess here and say that access_ok is intended to restrict user-space access, so it is probably ment to fail for memory belonging to the kernel (?) I guess the only fix is to create another function in filemap.c that has that call removed?
Is this correct or have I missed something?
Otherwise for my simple needs, removing the access_ok check works 'well enough'
Jason
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