kernel: Move memset of KPath buffer to after NULL check.

kernel: Initialize allocated KPath buffers to 0.

KPaths are most commonly used in the VFS syscall paths,
and so they are typically user_memcpy'd to/from userland.
In the "to" case this is not really necessary (but it should
be so small of a performance difference as to not matter),
but in the "from" case, we must always clear the buffer
we received from the allocator, so as not to leak information
to userland.

Part of #14961.

KPath: Use an object_cache for the path buffers in the normal case.

This was (following the packagefs changes) the number-one (by call
count) consumer of malloc() during the boot -- 52866 calls, and 100%
of them either 1024 or 1025 bytes!

Virtually all of these are ephemeral (indeed, the object_cache
stats after a boot with this patch shows there is only a single slab
of 64 buffers allocated, and most of them unused), so this is
probably a significant performance boost.

Change-Id: I659f5707510cbfeafa735d35eea7b92732ead666

KPath: Prevent setting a KPath to itself causing use-after-free.

SetTo frees the buffer before setting it to the new one,
but if KPath sets itself to ... itself, then it will of course
try to access the buffer again.

Spotted by clang-analyzer (amidst quite a few false positives,
so this doesn't seem like an especially good rabbit hole
to go down right now.)

KPathTest: Fix build for GCC 5.

* Also fixed a warning in KPath.
* Sorry, again!

KPath: Added LAZY_ALLOC flag.

* This allows KPath to not allocate a buffer when initialized
without path.
* Added test cases for this.
* Added test for LockBuffer().
* Enhanced tests to allow building them in debug mode.
* Moved calling vfs_normalize_path() into own private method.
* Improved error codes; B_NO_MEMORY is now only returned if the
allocation actually failed.
* If used with LAZY_ALLOC, Path() and LockBuffer() are now allowed
to return a NULL path.

KPath.Adopt(): Fixed path length.

* Issue was hidden due to inappropriate test values; changed test
to uncover it.

KPath: Replaced booleans with flags field.

* No functional change intended; I chose the flags in a way that it
should still work even if I missed a reference.

KPath: Fixed Normalize() return code, changed Leaf().

* Normalize() now returns the error code that vfs_normalize_path()
returns.
* Leaf() now returns "" instead of "/" for the root. It's not used
outside of KPath.
* Adapted RemoveLeaf() to deal with this correctly.
* "KPath = string" no longer changes the buffer size.
* Added missing operator tests for =, ==, and !=.

KPath.Adopt() fixed incorrect path/buffer length.

* The other object was left in an inconsistent state.
* This lets the unit test for Adopt() pass.

Minor style cleanup.

Ok there are some more, thanks Rene.

Coding style.

Normalize() didn't update fPathLength correctly. This did probably screw
up module image paths in module_init_post_boot_device(). Not sure whether
it also could cause #2776.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27760 a95241bf-73f2-0310-859d-f6bbb57e9c96

* vfs_normalize_path() and _user_normalize_path() use a common helper
function (normalize_path()), now. There was some code duplication
before.
* Added "bool traverseLink" parameter to vfs_normalize_path(). When
true and the leaf component is a symlink, it will be resolved.
* KPath:
- Added similar leaf link traversal parameter to SetTo() and
SetPath().
- Added Normalize().
- Added DetachBuffer(), which returns the object's current buffer and
unsets itself.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27751 a95241bf-73f2-0310-859d-f6bbb57e9c96

Honour 80 char/line limit.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25508 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Added Adopt() method that steals the other path's buffer.
* Fixed operator=(): the second argument of SetTo() is a boolean (normalize),
not the length of the buffer.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25382 a95241bf-73f2-0310-859d-f6bbb57e9c96

Reordered includes.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25376 a95241bf-73f2-0310-859d-f6bbb57e9c96

The second parameter of KPath::SetTo() is a bool, not a size_t. Reported
by Marc Flerackers. Thanks!


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25338 a95241bf-73f2-0310-859d-f6bbb57e9c96

Added RemoveLeaf() leaf method. Very handy for recursive directory
iteration code using a single KPath object.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@21606 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Reduced the stack usage of most of the I/O paths - there were several places
that put one or more full paths on the stack before, which could cause some
problems under certain conditions.
* Cleaned up KPath, ie. use size_t instead of int32 where appropriate, added
license.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@16585 a95241bf-73f2-0310-859d-f6bbb57e9c96

Renamed system/core to system/kernel.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12360 a95241bf-73f2-0310-859d-f6bbb57e9c96

Ok there are some more, thanks Rene.

Coding style.

Normalize() didn't update fPathLength correctly. This did probably screw
up module image paths in module_init_post_boot_device(). Not sure whether
it also could cause #2776.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27760 a95241bf-73f2-0310-859d-f6bbb57e9c96

* vfs_normalize_path() and _user_normalize_path() use a common helper
function (normalize_path()), now. There was some code duplication
before.
* Added "bool traverseLink" parameter to vfs_normalize_path(). When
true and the leaf component is a symlink, it will be resolved.
* KPath:
- Added similar leaf link traversal parameter to SetTo() and
SetPath().
- Added Normalize().
- Added DetachBuffer(), which returns the object's current buffer and
unsets itself.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27751 a95241bf-73f2-0310-859d-f6bbb57e9c96

Honour 80 char/line limit.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25508 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Added Adopt() method that steals the other path's buffer.
* Fixed operator=(): the second argument of SetTo() is a boolean (normalize),
not the length of the buffer.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25382 a95241bf-73f2-0310-859d-f6bbb57e9c96

Reordered includes.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25376 a95241bf-73f2-0310-859d-f6bbb57e9c96

The second parameter of KPath::SetTo() is a bool, not a size_t. Reported
by Marc Flerackers. Thanks!


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25338 a95241bf-73f2-0310-859d-f6bbb57e9c96

Added RemoveLeaf() leaf method. Very handy for recursive directory
iteration code using a single KPath object.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@21606 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Reduced the stack usage of most of the I/O paths - there were several places
that put one or more full paths on the stack before, which could cause some
problems under certain conditions.
* Cleaned up KPath, ie. use size_t instead of int32 where appropriate, added
license.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@16585 a95241bf-73f2-0310-859d-f6bbb57e9c96

Renamed system/core to system/kernel.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12360 a95241bf-73f2-0310-859d-f6bbb57e9c96