...@@footnote¹

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... ²

Present address: Zembu Labs, 445 Sherman Avenue, Palo Alto CA 94306, wrstuden@zembu.com

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...³

the fact that accessing non-resident portions of a file will block until the needed tape can be mounted and read. That will depend on the tape silo robotics, and, for tapes in off line storage, a human finding and mounting the needed tape. This delay, especially for off line storage, can be on the order of tens of minutes.

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... system⁴

file system mounted on /home, and an OVERLAY file system subsequently mounted on /home. Access to files under /home in the file name space (/home/user1/.profile for example) now go to the OVERLAY file system. It in turn can pass these to the underlying file system initially mounted on /home as it needs to. Contrast this to the case of mounting a second leaf (non-layered) file system onto /home. In this case, no operations would be passed to the file system initially mounted on /home until the second file system was unmounted.

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... behaved⁵

directly rather than using the bypass routine. It also checks for the case of a lookup of ``.'', where the returned vnode is the same as the vnode of the directory in which the lookup was performed and handles it explicitly.

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... subsystem⁶

detected by the presence of the IO_KNONBLOCK flag to the read, a flag set only by the NFS subsystem.

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... code⁷

this error code, its NFS client does not. Thus NFS exporting a DMFS layer to NetBSD clients will result in access to non-resident files returning errors to the application. Other NFS clients, such as the Solaris NFS client, will block the access and periodically retry it.

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