This patch changes the semantics of purgeable memory.
- AnonymousVMObject now has a "purgeable" flag. It can only be set when
constructing the object. (Previously, all anonymous memory was
effectively purgeable.)
- AnonymousVMObject now has a "volatile" flag. It covers the entire
range of physical pages. (Previously, we tracked ranges of volatile
pages, effectively making it a page-level concept.)
- Non-volatile objects maintain a physical page reservation via the
committed pages mechanism, to ensure full coverage for page faults.
- When an object is made volatile, it relinquishes any unused committed
pages immediately. If later made non-volatile again, we then attempt
to make a new committed pages reservation. If this fails, we return
ENOMEM to userspace.
mmap() now creates purgeable objects if passed the MAP_PURGEABLE option
together with MAP_ANONYMOUS. anon_create() memory is always purgeable.
Advisory locks don't actually prevent other processes from writing to
the file, but they do prevent other processes looking to acquire and
advisory lock on the file.
This implementation currently only adds non-blocking locks, which are
all I need for now.
We often get queried for the root inode, and it will always be cached
in memory anyway, so let's make Ext2FS::root_inode() fast by keeping
the root inode in a dedicated member variable.
To count the remaining children, we simply need to traverse the
directory and increment a counter. No need for a custom virtual that
all file systems have to implement. :^)
Unless we're accessing mutex-guarded metadata, there's no need to
acquire the inode lock.
The file system ID or inode index of a constructed inode will never
change, for example.
Reimplement directory traversal in terms of read_bytes() instead of
doing direct block access. This lets us avoid taking the inode lock
while iterating over the directory contents.
Once we've finalized all the file system metadata in flush_writes(),
we no longer need to hold the file system lock during the call to
BlockBasedFileSystem::flush_writes().
Ext2FS::get_inode() will remember unknown inode indices that it has
been asked about and put them into the inode cache as null inodes.
flush_writes() was not null-checking these while iterating, which
was a bug I finally managed to hit.
Flushing also seemed like a good time to drop unknown inodes from
the cache, since there's no good reason to hold to them indefinitely.
The file system lock is meant to protect the file system metadata
(super blocks, bitmaps, etc.) Not protect processes from reading
independent parts of the disk at once.
This patch introduces a new lock to protect the *block cache* instead,
which is the real thing that needs synchronization.
Forcing users of a FileDescription to seek before they can read/write
makes it inherently racy. This patch adds variants of read/write that
simply ignore the "current offset" of the description in favor of a
caller-supplied offset.
In case we are about to delete the PID directory, we clear the Process
pointer. If someone still holds a reference to the PID directory (by
opening it), we still need to delete the process, but we can't delete
the directory, so we will keep it alive, but any operation on it will
fail by propogating the error to userspace about that the Process was
deleted and therefore there's no meaning to trying to do operations on
the directory.
Fixes#8576.
We need some overflow checks due to the implementation of TmpFS.
When size_t is 32 bits and off_t is 64 bits, we might overflow our
KBuffer max size and confuse the KBuffer set_size code, causing a VERIFY
failure. Make sure that resulting offset + size will fit in a size_t.
Another constraint, we make sure that the resulting offset + size will
be less than half of the maximum value of a size_t, because we double
the KBuffer size each time we resize it.
Previously, VirtualFileSystem::mkdir() would always return ENOENT if
no parent custody was returned by resolve_path(). This is incorrect when
e.g. the user has no search permission in a component of the path
prefix (=> EACCES), or if on component of the path prefix is a file (=>
ENOTDIR). This patch fixes that behavior.
