libroot: fix path inconsistency in the find path API.

With the package kit merge, settings from packages were
placed into ~/config/settings/global for packages installed
into the PackageFS Home mount.

As a result, B_FIND_PATH_SETTINGS_DIRECTORY was returning a
user settings path different to the find directory API, making
transitioning from find directory to find path incompatible.

This change also updates the package_daemon and packagefs
to remove the remapping also occurring there.

Change-Id: Id5d077503e177a5f7cbc48779c132160b0d01890
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5941
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

use .IsSet() instead if .Get() != NULL

Change-Id: Ia2b7a719fd398e78cc3b11d4f7b02cb81179f65f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3488
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

file_systems: fs_read_link() doesn't use a user buffer

introduced in hrev26728 and hrev54107.

Change-Id: I3e98d54e829bcce559c43a8ee1abe4d889c0a571
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2819
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

storage/SymLink: Fix Be API regression in ReadLink

After this patch, "UnitTester BSymLink" passes.

BSymLink::ReadLink() in BeOS would always return the length of the
link unless an error occurred. Before this patch, Haiku instead seemed
to emulate posix readlink() behavior, returning the number of bytes
copied into the output buffer.

BeOS also did not guarantee that the string written into the output
buffer is NULL terminated if the output buffer cannot contain the
entire link contents, but the Haiku implementation does since it is is
a basic safety issue.

This patch fixes this and updates the Haiku API docs to describe the
behavior explicitly.

Fixing this required changing behavior in bfs_read_link, which
required changes in many more places.

docs/user/storage/SymLink.dox:
src/kits/storage/SymLink.cpp:
* Don't return B_BUFFER_OVERFLOW if the provided buffer is not large
enough to hold the link contents.
* Update documentation to clearly describe behavior.

src/add-ons/kernel/file_systems/bfs/kernel_interface.cpp:
* Change bfs_read_link() to always return the link length. This is
called by common_read_link in the VFS, which is called by
_kern_read_link().

src/add-ons/kernel/file_systems/btrfs/kernel_interface.cpp:
src/add-ons/kernel/file_systems/exfat/kernel_interface.cpp:
src/add-ons/kernel/file_systems/ext2/kernel_interface.cpp:
src/add-ons/kernel/file_systems/iso9660/kernel_interface.cpp:
src/add-ons/kernel/file_systems/netfs/client/netfs.cpp:
src/add-ons/kernel/file_systems/nfs/nfs_add_on.c:
src/add-ons/kernel/file_systems/ramfs/kernel_interface.cpp:
src/add-ons/kernel/file_systems/reiserfs/Iterators.cpp:
src/add-ons/kernel/file_systems/reiserfs/Iterators.h:
src/add-ons/kernel/file_systems/reiserfs/Volume.cpp:
src/add-ons/kernel/file_systems/reiserfs/Volume.h:
* Update the implementation of read_link for these filesystems. Some
of them were incorrect, and some had just copied the posix behavior of
bfs from before this patch.
* Use user_memcpy in ext2_read_link()
* Use user_memcpy in nfs fs_read_link()
* Use user_memcpy in reiserfs StreamReader::_ReadIndirectItem and
StreamReader::_ReadDirectItem
* Remove unused method Volume::ReadObject in reiserfs.

src/add-ons/kernel/file_systems/packagefs/nodes/UnpackingLeafNode.cpp:
src/add-ons/kernel/file_systems/packagefs/package_links/PackageLinkSymlink.cpp:
* Update UnpackingLeafNode::ReadSymlink and
PackageSymLink::ReadSymLink() to set the bufferSize out parameter to
the symlink length. Both of these are called by
packagefs_read_symlink.
* Use user_memcpy

src/add-ons/kernel/file_systems/netfs/client/netfs.cpp:
* netfs seems mostly unimplemented. Added a FIXME note for future
implementers so that they know to implement the correct behavior.

src/system/libroot/posix/unistd/link.c:
* readlinkat() was just wrapping _kern_read_link() because before this
patch it had expected posix behavior. But now it does not, so we
need to return the number of bytes written to the output
buffer.

src/build/libroot/fs.cpp:
* Update _kern_read_link() in the compatibility code to emulate the
Haiku behavior on the host system. This is done by using an
intermediate buffer that is guaranteed to fit the link contents and
returning its length. The intermediate buffer is copied into the
output buffer until there is no more room.

src/tests/kits/storage/SymLinkTest.cpp:
* This patch also resolves some test failures similar to those
resolved in ee8cf35f0 which fixed tests for BNode. The tests were
failing because Haiku's error checking is just better.

BeOS allowed constructing a BSymLink with BSymLink(BDirectory*,
const char*) with the entry name of "". The same is true of the
equivilant SetTo() method. The BSymLink object will appear valid
until you attempt to use it by, for example, calling the ReadLink
method, which will return B_BAD_VALUE.

Haiku does a more appropriate thing and returns B_ENTRY_NOT_FOUND,
for this constructor and the equivilant SetTo(BDirectory*, const
char*) method. This patch fixes these test assertions to match Haiku
behavior.

docs/develop/file_systems/overview.txt:
* Add notes for future filesystem driver implementers to call this
mistake when implementing fs_vnode_ops::read_symlink.

docs/user/drivers/fs_interface.dox:
* Fix documentation for fs_vnode_ops::read_symlink

Change-Id: I8bcb8b2a0c9333059c84ace15844c32d4efeed9d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2502
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Axel Dörfler <axeld@pinc-software.de>

packagefs: Automatic package attributes for packages symlinks

Add automatically generated attributes "SYS:PACKAGE" and
"SYS:PACKAGE_FILE" to the /packages/... directories and symlinks.

packagefs: PackageLinkSymlink: Fix crash on custom mount

Remove /boot/common for good

* Remove support for the "common" installation location from packagefs,
package kit, package daemon, package managers.
* Rename the B_COMMON_*_DIRECTORY constants referring to writable
directories to B_SYSTEM_*_DIRECTORY.
* Remove/adjust the use of various B_COMMON_*_DIRECTORY constants.
I'm sure some occurrence still remain. They can be adjusted when the
remaining B_COMMON_*_DIRECTORY constants are removed.

Initial changes to remove /boot/common

* find_directory() and hard-coded paths use /boot/system instead of
/boot/common.
* The build system creates the writable directories in /boot/system
instead of /boot/common.
* The build system no longer installs any packages in /boot/common.

packagefs: Share string instances globally

Introduce a class String which refers to shared private data that is
registered in a global hash table (in class StringPool) and use the
class consequently. This eliminates duplicate allocations for the same
string and also speeds up tests for equality. There's quite a bit
overhead for the management structures (apparently even more than for
the string data itself), but due to almost all strings being used
multiple times this still almost halves the memory usage for string
data.

packagefs: Organize sources into subdirectories

packagefs: Automatic package attributes for packages symlinks

Add automatically generated attributes "SYS:PACKAGE" and
"SYS:PACKAGE_FILE" to the /packages/... directories and symlinks.

packagefs: PackageLinkSymlink: Fix crash on custom mount

Remove /boot/common for good

* Remove support for the "common" installation location from packagefs,
package kit, package daemon, package managers.
* Rename the B_COMMON_*_DIRECTORY constants referring to writable
directories to B_SYSTEM_*_DIRECTORY.
* Remove/adjust the use of various B_COMMON_*_DIRECTORY constants.
I'm sure some occurrence still remain. They can be adjusted when the
remaining B_COMMON_*_DIRECTORY constants are removed.

Initial changes to remove /boot/common

* find_directory() and hard-coded paths use /boot/system instead of
/boot/common.
* The build system creates the writable directories in /boot/system
instead of /boot/common.
* The build system no longer installs any packages in /boot/common.

packagefs: Share string instances globally

Introduce a class String which refers to shared private data that is
registered in a global hash table (in class StringPool) and use the
class consequently. This eliminates duplicate allocations for the same
string and also speeds up tests for equality. There's quite a bit
overhead for the management structures (apparently even more than for
the string data itself), but due to almost all strings being used
multiple times this still almost halves the memory usage for string
data.

packagefs: Organize sources into subdirectories