As with the previous commit, we put a distinction between filesystems
that require a file description and those which don't, but now in a much
more readable mechanism - all initialization properties as well as the
create static method are grouped to create the FileSystemInitializer
structure. Then when we need to initialize an instance, we iterate over
a table of these structures, checking for matching structure and then
validating the given arguments from userspace against the requirements
to ensure we can create a valid instance of the requested filesystem.
This is important for dmidecode because it does an fstat on the DMI
blobs, trying to figure out their size. Because we already know the size
of the blobs when creating the SysFS components, there's no performance
penalty whatsoever, and this allows dmidecode to not use the /dev/mem
device as a fallback.
Instead, allocate before constructing the object and pass NonnullOwnPtr
of KString to the object if needed. Some classes can determine their
names as they have a known attribute to look for or have a static name.
We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace!
This was a slightly tedious refactoring that took a long time, so it's
not unlikely that some bugs crept in.
Nevertheless, it does pass basic functionality testing, and it's just
real nice to finally see the same pattern in all contexts. :^)
Normally, trying to truncate a SysFSInode should result in EPERM error.
However, as suggested by Ali (@alimpfard), we can allow the PowerState
node to be "truncated" so one can open that file with O_TRUNC option.
Likewise, we also need to provide a way to set modified time on SysFS
inodes. For most inodes, we should return ENOTIMPL error, but for the
power state switch, we ignore the modified time setting and just return
KSuccess.
These fixes allow to do "echo -n 1 > /sys/firmware/power_state" in Shell
after gaining root permissions, to switch the power state.
These files are not marked as block devices or character devices so they
are not meant to be used as device nodes. The filenames are formatted to
the pattern "major:minor", but a Userland program need to call the parse
these format and inspect the the major and minor numbers and create the
real device nodes in /dev.
Later on, it might be a good idea to ensure we don't create new
SysFSComponents on the heap for each Device, but rather generate
them only when required (and preferably to not create a SysFSComponent
at all if possible).
- Use KResultOr and TRY() to propagate errors
- Check for OOM errors
- Move allocation out of constructors
There's still a lot more to do here, as SysFS is still quite brittle
in the face of memory pressure.
Like with the ProcFS, description data can change at anytime, so it's
wise to ensure that when the userland reads from an Inode, data is
consistent unless the userland indicated it wants to refresh the data
(by seeking to offset 0, or re-attaching the Inode).
Otherwise, if the data changes in the middle of the reading, it can
cause silent corruption in output which can lead to random crashes.
Prior to this change, both uid_t and gid_t were typedef'ed to `u32`.
This made it easy to use them interchangeably. Let's not allow that.
This patch adds UserID and GroupID using the AK::DistinctNumeric
mechanism we've already been employing for pid_t/ProcessID.
The intention is to add dynamic mechanism for notifying the userspace
about hotplug events. Currently, the DMI (SMBIOS) blobs and ACPI tables
are exposed in the new filesystem.
