libfsdriver: clear VM cache only if used

As part of its built-in mmap emulation support for "none" file system
services, libfsdriver clears the VM cache upon exit. However, for
trivial file systems

libfsdriver: clear VM cache only if used

As part of its built-in mmap emulation support for "none" file system
services, libfsdriver clears the VM cache upon exit. However, for
trivial file systems which do not even support reading from files, the
the VM cache need to be cleared either. With this patch, the VM cache
is cleared only when modified, so that such trivial file systems need
not be given CLEARCACHE permission.

Change-Id: I518c092443455302b9b9728f10a3f894d2c8036b

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libfsdriver: default to noop for putnode

While putnode requests should always succeed, very simple file system
services may not care about reference counts and thus about putnode
requests at all. F

libfsdriver: default to noop for putnode

While putnode requests should always succeed, very simple file system
services may not care about reference counts and thus about putnode
requests at all. For this reason, we now default to an OK response if
no fdr_putnode implementation is given.

Change-Id: I01f6421abf4546a1f69d8c21900a92d6acc45745

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libfsdriver: preinitialize stat.st_ino

The stat.st_ino field must always be filled with the inode number
given as part of the fdr_stat request anyway, so libfsdriver can
simply fill in the number an

libfsdriver: preinitialize stat.st_ino

The stat.st_ino field must always be filled with the inode number
given as part of the fdr_stat request anyway, so libfsdriver can
simply fill in the number and allow the file system not to bother.

Change-Id: Ia7a849d0b23dfc83010df0d48fa26e4225427694

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libfsdriver: support mmap on FSes with no device

This patch adds (very limited) support for memory-mapping pages on
file systems that are mounted on the special "none" device and that
do not impleme

libfsdriver: support mmap on FSes with no device

This patch adds (very limited) support for memory-mapping pages on
file systems that are mounted on the special "none" device and that
do not implement PEEK support by themselves. This includes hgfs,
vbfs, and procfs.

The solution is implemented in libvtreefs, and consists of allocating
pages, filling them with content by calling the file system's READ
functionality, passing the pages to VM, and freeing them again. A new
VM flag is used to indicate that these pages should be mapped in only
once, and thus not cached beyond their single use. This prevents
stale data from getting mapped in without the involvement of the file
system, which would be problematic on file systems where file contents
may become outdated at any time. No VM caching means no sharing and
poor performance, but mmap no longer fails on these file systems.

Compared to a libc-based approach, this patch retains the on-demand
nature of mmap. Especially tail(1) is known to map in a large file
area only to use a small portion of it.

All file systems now need to be given permission for the SETCACHEPAGE
and CLEARCACHE calls to VM.

A very basic regression test is added to test74.

Change-Id: I17afc4cb97315b515cad1542521b98f293b6b559

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libfsdriver: prefill st_dev for stat requests

This obviates the need for several file system implementations to
remember the device on which they are mounted.

Change-Id: Ida8325cf4bcf072e61761cfee3

libfsdriver: prefill st_dev for stat requests

This obviates the need for several file system implementations to
remember the device on which they are mounted.

Change-Id: Ida8325cf4bcf072e61761cfee34e3f7ed2d750b9

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Add libfsdriver: a library to drive file systems

This library provides new abstractions for the upper (VFS) side of
file system services, and should be used for all file system service
implementatio

Add libfsdriver: a library to drive file systems

This library provides new abstractions for the upper (VFS) side of
file system services, and should be used for all file system service
implementations from now on. It provides the following functionality:

- a function call table abstraction, hiding the details of the
VFS-FS protocol with simple parameters;
- a (currently limited) number of per-function steps required for
all file system implementations, such as copying in and out path
names and result buffers;
- a default implementation for multicomponent path lookups, such
that the file system merely has to implement resolution of single
components at a time;
- an abstraction for copying data from and to the file system, which
allows transparent intraprocess copying as required for the lookup
implementation;
- a set of functions to simplify getdents implementations.

The message loop provided by the library is currently for use by
single-threaded file system implementations only. Multithreaded file
system services may use the more low-level message processing
functionality.

Protocol-level optimizations such as including names in protocol
messages may be hidden entirely in this library. In addition, in the
future, the lookup implementation may be replaced by a single-
component lookup VFS/FS protocol request as part of a VFS name cache
implementation; this, too, can be hidden entirely in this library.

Change-Id: Ib34f0d0e021dfa3426ce8826efcf3eaa94d3ef3e

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