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6 Related Work

  The idea of dynamic or variable pathname components is not new. HP-UX does this with context-dependent files[8], and Mach with the `` @SYS'' variables[4]. Both of these implementations support replacement of pathname components by kernel variables. Apollo's DOMAIN/OS supported a more sophisticated system where arbitrary user environment variables could be referenced in pathnames[11,12]. On the issue of having a user's home files and mailbox file reside in one location, Plan 9's attach operator can be used to unify several file servers into one user name space[14].

What is new about our idea is that we do not require any change to any part of the filesystem implementation in the kernel. All that is required are RPC and NFS, making the system much more widely applicable.

Though at first it may appear that amd can do what hlfsd does, it can't. Amd cannot return different pathnames as a value of a symbolic link depending on who accessed it. See also Section 2.3 for more details on various ways in which amd cannot help the way hlfsd can.

6.1 Mail-reading Servers

  The future of mail reading and sending may be similar to that used by the NNTP protocol used for managing NetNews[10,19]. That is, a special-purpose server which provides network connections for reading and writing mail remotely.

Several such programs exist, most notably IMAP[16] and POP[17]. However, use of these servers is limited at this time because most MTAs and UAs have not been converted to use them, or they require special environments (the Andrew Message Delivery System[18] requires AFS). Porting those applications for most popular environments is not going to be an easy task. Nevertheless, the benefits of such services over that of hlfsd would include faster and more reliable service, plus greatly expanded functionality (possibly providing threads information for threaded mail readers).

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Next: 7 Conclusion Up: HLFSD: Delivering Email to Previous: 5 Evaluation
Erez Zadok