Cygwin for Windows 8
Wed Oct 17 09:51:00 GMT 2012
On Oct 17 09:03, GrahamC wrote:
> On Oct 16 Corinna Vinschen wrote:
> > On Oct 15 23:55, GrahamC wrote:
> > > Another anomaly with disk drive partition devices (/dev/sdX1, /dev/sdX2 etc.) is the access control.
> > > Â
> > > While the whole disk devices (/dev/sdX) can only be accessed when running as administrator, the
> > > individual partition devices (/dev/sdX1, /dev/sdX2 etc.)Â can be both read and written without
> > > needing administrator mode.
> > Access control is not done inside Cygwin.Â The permissions on the block
> > devices are set by Windows.Â If you want to take a closer look,Â see
> > the mapping of the native namespace into the Cygwin /proc/sys namespace.
> > Look at everything under /proc/sys/Device/Harddisk*, but make sure you're
> > admin, otherwise you won't see everything.Â If you want to take an even
> > closer look, I suggest to download the winobj tool from sysinternal.Â It
> > also provides a detailed ACL view.
> > Device creation is based on what Windows creates. Cygwin only looks
> > which devices exist in the internal native namespace and maps those to
> > the equivalent POSIX device names.Â If a \Device\HarddiskX\PartitionY
> > exists, then /dev/sd<X>Y exists in Cygwin, with <X> being 'a' + X.
> > As for the missing ~70 sectors, I'm not sure.Â How do you know?Â Does
> > the number of KBs you can read differ by this amount from the KBs given
> > in /proc/partitions?Â
> > Maybe that's the missing call to FSCTL_ALLOW_EXTENDED_DASD_IO.Â Cygwin's
> > block device code only calls this Windows ioctl code for full disks, not
> > for partitions on the disk.Â I fixed that in CVS, though.Â Can you give
> > the today's snapshot from http://cygwin.com/snapshots/ a try, please?
> OK, the 20121016 snapshot of cygwin1.dll fixed the data truncation
> problem. The number of sectors readable from the /dev/sdXY
> devices now match the partition sizes.
I'm very glad to read that.
> My missing partition devices appears to be an incompatibility between
> the Linux parted tool and Windows. The former puts a 6 byte disk ID in the
> partition sector at position 0x1b8..0x1bd, Windows uses the first 4 bytes only
> and if two disks have the same value it doesn't create volumes for the second disk.
> Patching the ID to a unique value in the first 4 bytes made the missing partitions
> appear at next boot up.
In theory you should be able to get away without reboot. There's
a diskpart command available since at least XP. Diskpart knows a
"rescan" command, which tells the OS to rescan the disks and see
if anything changed.
> Non-administrator read and write access to /dev/sdXY devices appears to
> be limited to the USB flash devices.
Yeah, I had a hunch that it was related to the disk type (fixed vs.
> The WinObj tool shows the
> group INTERACTIVE having read and write access to these. I suppose this
> makes sense from the Windows point of view. WinObj also shows group
> Everyone has read access to the raw disk devices DR0, DR1, DR2 etc.,
> but that doesn't seem to make it through to the /dev/sdX devices (not
> that I would want it to).
Yes, that puzzled me as well, but it makes sense.
The ACL information given in winobj is not as detailed as I had hoped
for. In fact, "Everyone" only has READ_CONTROL and FILE_READ_ATTRIBUTE
permissions, but *not* FILE_READ_DATA. If you try to open anything for
reading, Cygwin requests GENERIC_READ permissions which obviously
includes FILE_READ_DATA permissions as well. Naturally, that fails with
So, in fact a non-admin can get meta information about a block device
(think "stat"), but can not open the device for reading. And,
surprisingly, this time the Cygwin information is more correct than the
$ ls -l /proc/sys/Device/Harddisk0/DR0
brwxrwx--x 1 Administrators SYSTEM 0, 250 Oct 17 11:49 /proc/sys/Device/Harddisk0/DR0
As you can see, no read permissions for "Other"
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
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