similar to: [PATCH v2] virtio-rng: return available data with O_NONBLOCK

On 11/08/2020 15:14, Michael S. Tsirkin wrote: > On Tue, Aug 11, 2020 at 03:00:14PM +0200, Laurent Vivier wrote: >> No problem. This code is tricky and it took me several months to really >> start to understand it ... > > Oh great, we actually have someone who understands the code! > Maybe you can help me understand: virtio_read > takes the buf pointer and puts it in

On 11/08/2020 15:14, Michael S. Tsirkin wrote: > On Tue, Aug 11, 2020 at 03:00:14PM +0200, Laurent Vivier wrote: >> No problem. This code is tricky and it took me several months to really >> start to understand it ... > > Oh great, we actually have someone who understands the code! > Maybe you can help me understand: virtio_read > takes the buf pointer and puts it in

On 11/08/2020 14:22, Martin Wilck wrote: > On Tue, 2020-08-11 at 14:02 +0200, Laurent Vivier wrote: >> >>>> drivers/char/hw_random/virtio-rng.c | 14 ++++++++++++++ >>>> 1 file changed, 14 insertions(+) >>>> >>>> diff --git a/drivers/char/hw_random/virtio-rng.c >>>> b/drivers/char/hw_random/virtio-rng.c >>>> index

On 11/08/2020 16:28, mwilck at suse.com wrote: > From: Martin Wilck <mwilck at suse.com> > > If a program opens /dev/hwrng with O_NONBLOCK and uses poll() and > non-blocking read() to retrieve random data, it ends up in a tight > loop with poll() always returning POLLIN and read() returning EAGAIN. > This repeats forever until some process makes a blocking read() call.

On 11/08/2020 16:28, mwilck at suse.com wrote: > From: Martin Wilck <mwilck at suse.com> > > If a program opens /dev/hwrng with O_NONBLOCK and uses poll() and > non-blocking read() to retrieve random data, it ends up in a tight > loop with poll() always returning POLLIN and read() returning EAGAIN. > This repeats forever until some process makes a blocking read() call.

On 28/08/2020 23:34, Martin Wilck wrote: > On Wed, 2020-08-26 at 08:26 -0400, Michael S. Tsirkin wrote: >> On Tue, Aug 11, 2020 at 04:42:32PM +0200, Laurent Vivier wrote: >>> On 11/08/2020 16:28, mwilck at suse.com wrote: >>>> From: Martin Wilck <mwilck at suse.com> >>>> >>>> If a program opens /dev/hwrng with O_NONBLOCK and uses poll()

On 11/08/2020 12:37, Philippe Mathieu-Daud? wrote: > You Cc'ed qemu-devel, so Cc'ing the virtio-rng maintainers. > > On 7/15/20 3:32 PM, mwilck at suse.com wrote: >> From: Martin Wilck <mwilck at suse.com> >> >> If a program opens /dev/hwrng with O_NONBLOCK and uses poll() and >> non-blocking read() to retrieve random data, it ends up in a tight

There's currently a big lock around everything, and it means that we can't query sysfs (eg /sys/devices/virtual/misc/hw_random/rng_current) while the rng is reading. This is a real problem when the rng is slow, or blocked (eg. virtio_rng with qemu's default /dev/random backend) This doesn't help (it leaves the current lock untouched), just adds a lock to protect the read function

On Wed, Jul 15, 2020 at 03:32:55PM +0200, mwilck at suse.com wrote: > From: Martin Wilck <mwilck at suse.com> > > If a program opens /dev/hwrng with O_NONBLOCK and uses poll() and > non-blocking read() to retrieve random data, it ends up in a tight > loop with poll() always returning POLLIN and read() returning EAGAIN. > This repeats forever until some process makes a

Amos Kong <akong at redhat.com> writes: > I started a QEMU (non-smp) guest with one virtio-rng device, and read > random data from /dev/hwrng by dd: > > # dd if=/dev/hwrng of=/dev/null & > > In the same time, if I check hwrng attributes from sysfs by cat: > > # cat /sys/class/misc/hw_random/rng_* > > The cat process always gets stuck with slow backend (5

Amos Kong <akong at redhat.com> writes: > I started a QEMU (non-smp) guest with one virtio-rng device, and read > random data from /dev/hwrng by dd: > > # dd if=/dev/hwrng of=/dev/null & > > In the same time, if I check hwrng attributes from sysfs by cat: > > # cat /sys/class/misc/hw_random/rng_* > > The cat process always gets stuck with slow backend (5

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My hotplug tests: | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: | guest) # dd if=/dev/random of=/dev/null & | hotunplug rng device from qemu monitor | | test

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My hotplug tests: | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: | guest) # dd if=/dev/random of=/dev/null & | hotunplug rng device from qemu monitor | | test

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My hotplug tests: | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: | guest) # dd if=/dev/random of=/dev/null & | hotunplug rng device from qemu monitor | | test

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My hotplug tests: | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: | guest) # dd if=/dev/random of=/dev/null & | hotunplug rng device from qemu monitor | | test

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My original was pain, Rusty posted a real fix. This patchset fixed two issue in v1, and tested by my 6+ cases. | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: |

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My original was pain, Rusty posted a real fix. This patchset fixed two issue in v1, and tested by my 6+ cases. | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: |

A bit late to a party, but: On Mon, Dec 8, 2014 at 12:50 AM, Amos Kong <akong at redhat.com> wrote: > From: Rusty Russell <rusty at rustcorp.com.au> > > There's currently a big lock around everything, and it means that we > can't query sysfs (eg /sys/devices/virtual/misc/hw_random/rng_current) > while the rng is reading. This is a real problem when the rng is

A bit late to a party, but: On Mon, Dec 8, 2014 at 12:50 AM, Amos Kong <akong at redhat.com> wrote: > From: Rusty Russell <rusty at rustcorp.com.au> > > There's currently a big lock around everything, and it means that we > can't query sysfs (eg /sys/devices/virtual/misc/hw_random/rng_current) > while the rng is reading. This is a real problem when the rng is

On Tue, Aug 11, 2020 at 02:07:23PM +0200, Martin Wilck wrote: > On Tue, 2020-08-11 at 07:26 -0400, Michael S. Tsirkin wrote: > > On Wed, Jul 15, 2020 at 03:32:55PM +0200, mwilck at suse.com wrote: > > > drivers/char/hw_random/virtio-rng.c | 14 ++++++++++++++ > > > 1 file changed, 14 insertions(+) > > > > > > diff --git