Hi folks,
I noticed a strange discrepancy when running Cygwin through mintty, vs
through a normal cmd.exe console. This is on a build from the latest
git master, but also on Cygwin 2.8.0. When run from a cmd.exe
console, we can see the following output from fhandler_dev::readdir:
$ ls -l /dev/con*
crw-rw-rw- 4 Erik M. Bray Erik M. Bray 3, 0 Aug 22 18:29 /dev/conin
crw-rw-rw- 4 Erik M. Bray Erik M. Bray 3, 0 Aug 22 18:29 /dev/conout
crw-rw-rw- 4 Erik M. Bray Erik M. Bray 3, 0 Aug 22 18:29 /dev/cons0
crw-rw-rw- 4 Erik M. Bray Erik M. Bray 3, 0 Aug 22 18:29 /dev/console
The same command when run in mintty returns:
crw-rw-rw- 1 Erik M. Bray Erik M. Bray 5, 255 Aug 22 18:29 /dev/conin
crw-rw-rw- 1 Erik M. Bray Erik M. Bray 5, 254 Aug 22 18:29 /dev/conout
crw-rw-rw- 1 Erik M. Bray Erik M. Bray 5, 1 Aug 22 18:29 /dev/console
In the latter case, the device numbers are the default device numbers
for /dev/console, etc. In the former case, the inodes for
/dev/console, /dev/conin, and /dev/conout are set to the same as
/dev/cons0. This logic can be found in fhandler_dev::readdir:
203 if (cdev->get_major () == DEV_TTY_MAJOR
204 && (cdev->is_device (FH_CONIN)
205 || cdev->is_device (FH_CONOUT)
206 || cdev->is_device (FH_CONSOLE)))
207 {
208 /* Make sure conin, conout, and console have the same inode number
209 as the current consX. */
210 de->d_ino = myself->ctty;
211 }
where myself->ctty seems to depend largely on what file types the
stdio handles are attached to.
When running from cmd.exe, GetStdHandle(...) returns handles to a
character stream--i.e. the console itself. However, when running from
mintty it returns pipes (specifically, to a pty, probably related to
the call to forkpty in mintty). In Cygwin (particularly, in
dtable::init_std_file_from_handle) the result ends up being that when
the stdio handles are pipes, the /dev/cons0 device never gets created.
And thus /dev/console and friends never get rerouted to a real device.
This results in errors when trying to access /dev/console directly:
$ ls -l /dev/console
ls: cannot access '/dev/console': No such device or address
which is the error message for a ENXIO. This is coming specifically
from the function build_fh_pc in dtable.cc. The reason is that trying
to access /dev/console results in trying to create an fhandler_console
for a non-existent console.
I'm not really sure what the correct behavior should be here though,
and if it should be fixed on the mintty side or the Cygwin side.
Thanks,
Erik
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