This patch introduces a new scheme of handling ioctl operations that
maps ioctls to pseudo-file accesses, similar to how the libc maps socket
calls to socket-fs operations.
A device file can be accompanied with a (hidden) directory that is named
after the device file and hosts pseudo files for triggering the various
device operations. For example, for accessing a terminal, the directory
structure looks like this:
/dev/terminal
/dev/.terminal/info
The 'info' file contains device information in XML format. The type of
the XML node corresponds to the device type. E.g., If the libc receives
a 'TIOCGWINSZ' ioctl for /dev/terminal, it reads the content of
/dev/.terminal/info to obtain the terminal-size information. In this
case, the 'info' file looks as follows:
<terminal rows="25" columns="80/>
Following this scheme, VFS plugins can support ioctl operations by
providing an ioctl directory in addition to the actual device file.
Internally, the mechanism uses the 'os/vfs.h' API to access pseudo
files. Hence, we need to propagate the Vfs::Env to 'vfs_plugin.cc' to
create an instance of a 'Directory' for the root for the VFS.
Issue #3519
7ac32ea60c