VM: allocate cache pages in mmap region

That way, these pages are transferred during live update, as they
should. This resolves a mfs crash after a number of live updates.

Change-Id: Ia53bec2692b2

VM: allocate cache pages in mmap region

That way, these pages are transferred during live update, as they
should. This resolves a mfs crash after a number of live updates.

Change-Id: Ia53bec2692b2114c29b96a453beb0f915f56453a

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vm: Allow in-band metadata for cache blocks

Allow extra space for in-band metadata when allocating cache blocks.

Edited by David van Moolenbroek: since this effectively halves the
potential size of

vm: Allow in-band metadata for cache blocks

Allow extra space for in-band metadata when allocating cache blocks.

Edited by David van Moolenbroek: since this effectively halves the
potential size of the typical file system cache, do this only when
compiling with instrumentation.

Change-Id: I0840af6420899ede2d5bb7539e79c0a456b5128d

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libminixfs: better support for read errors and EOF

- The lmfs_get_block*(3) API calls may now return an error. The idea
is to encourage a next generation of file system services to do a
better

libminixfs: better support for read errors and EOF

- The lmfs_get_block*(3) API calls may now return an error. The idea
is to encourage a next generation of file system services to do a
better job at dealing with block read errors than the MFS-derived
implementations do. These existing file systems have been changed
to panic immediately upon getting a block read error, in order to
let unchecked errors cause corruption. Note that libbdev already
retries failing I/O operations a few times first.

- The libminixfs block device I/O module (bio.c) now deals properly
with end-of-file conditions on block devices. Since a device or
partition size may not be a multiple of the root file system's block
size, support for partial block retrival has been added, with a new
internal lmfs_get_partial_block(3) call. A new test program,
test85, tests the new handling of EOF conditions when reading,
writing, and memory-mapping a block device.

Change-Id: I05e35b6b8851488328a2679da635ebba0c6d08ce

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libminixfs/VM: fix memory-mapped file corruption

This patch employs one solution to resolve two independent but related
issues. Both issues are the result of one fundamental aspect of the
way VM's

libminixfs/VM: fix memory-mapped file corruption

This patch employs one solution to resolve two independent but related
issues. Both issues are the result of one fundamental aspect of the
way VM's memory mapping works: VM uses its cache to map in blocks for
memory-mapped file regions, and for blocks already in the VM cache, VM
does not go to the file system before mapping them in. To preserve
consistency between the FS and VM caches, VM relies on being informed
about all updates to file contents through the block cache. The two
issues are both the result of VM not being properly informed about
such updates:

1. Once a file system provides libminixfs with an inode association
(inode number + inode offset) for a disk block, this association
is not broken until a new inode association is provided for it.
If a block is freed and reallocated as a metadata (non-inode)
block, its old association is maintained, and may be supplied to
VM's secondary cache. Due to reuse of inodes, it is possible
that the same inode association becomes valid for an actual file
block again. In that case, when that new file is memory-mapped,
under certain circumstances, VM may end up using the metadata
block to satisfy a page fault on the file, due to the stale inode
association. The result is a corrupted memory mapping, with the
application seeing data other than the current file contents
mapped in at the file block.

2. When a hole is created in a file, the underlying block is freed
from the device, but VM is not informed of this update, and thus,
if VM's cache contains the block with its previous inode
association, this block will remain there. As a result, if an
application subsequently memory-maps the file, VM will map in the
old block at the position of the hole, rather than an all-zeroes
block. Thus, again, the result is a corrupted memory mapping.

This patch resolves both issues by making the file system inform the
minixfs library about blocks being freed, so that libminixfs can
break the inode association for that block, both in its own cache and
in the VM cache. Since libminixfs does not know whether VM has the
block in its cache or not, it makes a call to VM for each block being
freed. Thus, this change introduces more calls to VM, but it solves
the correctness issues at hand; optimizations may be introduced
later. On the upside, all freed blocks are now marked as clean,
which should result in fewer blocks being written back to the device,
and the blocks are removed from the caches entirely, which should
result in slightly better cache usage.

This patch is necessary but not sufficient to resolve the situation
with respect to memory mapping of file holes in general. Therefore,
this patch extends test 74 with a (rather particular but effective)
test for the first issue, but not yet with a test for the second one.

This fixes #90.

Change-Id: Iad8b134d2f88a884f15d3fc303e463280749c467

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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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New sources layout

Change-Id: Ic716f336b7071063997cf5b4dae6d50e0b4631e9