On 1/17/2017 11:49 AM, David Howells wrote: > David Howells <dhowells@xxxxxxxxxx> wrote: > >> AFS filesystem implementations like OpenAFS have a number of management calls >> usually implemented through the pioctl() and afs() system calls. However, >> there is general revulsion to the idea of allowing these in Linux as they are >> very much abused. >> >> Now, I need to come up with replacements for these. For some I can use >> getxattr()/setxattr(), for some keyrings and for others procfs/sysfs, but for >> some I can't. >> >> One of these is the call to manage local caching on a file or volume. This, >> however, doesn't really need to be limited to AFS, but could also be >> applicable to NFS, CIFS, etc. - and possibly even to local filesystems. >> >> A brainstorming session on this would be useful. I would be happy to participate. > Another thing that I would like to work out is how to do mountpoint management > commands for kAFS. This includes doing the following operations: > > (*) Creating a mountpoint. > > (*) Deleting a mountpoint > > (*) Reading a mountpoint. > > (*) Invalidating cached mountpoint information. > > The problem here is that mountpoints are automatically mounted when you touch > them unless you specify the AT_NO_AUTOMOUNT flag - and even then, that's > ignored if the mountpoint is already mounted upon. > > I could do this by saying that you have to open the parent directory of the > mountpoint and do an ioctl() on it, but would it be better to have one or more > syscalls for this purpose? I am uncomfortable with opening the parent directory object because it introduces object reference confusion when the path to the parent directory is itself a symlink or a mount point. Granted, the AFS3 protocol does not make this easy. 1. An AFS3 mount point is a special type of symlink 2. AFS3 does not provide a method by which a symlink's target can be altered or its type changed after it is created. 3. Legacy AFS3 clients have always exposed mount points to applications as a directory not a symlink. If I had my preference, I would implement creating a mount point as: 1. create an empty file or symlink 2. open the resulting object and issue an ioctl against that object to set a mount point target which results in it becoming a mount point. Deleting, Reading, Modifying, and Invalidating all are implemented as 1. open mount point 2. issue ioctl against object Unfortunately, AFS3 simply doesn't provide the functionality I desire. The best that could be done would be to implement a createMountPoint ioctl which operates by deleting the open object and creating a new mount point object in its place. While dealing with the fact that the AFS FID for the object object will change as a result. > > Further, would this be of use to any other filesystems? Could SMB use this as a method of defining referrals? Jeffrey Altman
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