On Wed, Mar 3, 2021 at 10:18 AM Cornelia Huck <[email protected]> wrote:
>
> On Mon, 1 Mar 2021 10:51:03 -0700
> Enrico Granata <[email protected]> wrote:
>
> > In many embedded systems, virtio-blk implementations are
> > backed by eMMC or UFS storage devices, which are subject to
> > predictable and measurable wear over time due to repeated write
> > cycles.
> >
> > For such systems, it can be important to be able to track
> > accurately the amount of wear imposed on the storage over
> > time and surface it to applications. In a native deployments
> > this is generally handled by the physical block device driver
> > but no such provision is made in virtio-blk to expose these
> > metrics for devices where it makes sense to do so.
> >
> > This patch adds support to virtio-blk for lifetime and wear
> > metrics to be exposed to the guest when a deployment of
> > virtio-blk is done over compatible eMMC or UFS storage.
> >
> > Signed-off-by: Enrico Granata <[email protected]>
> > ---
> > content.tex | 31 +++++++++++++++++++++++++++++--
> > 1 file changed, 29 insertions(+), 2 deletions(-)
> >
> > diff --git a/content.tex b/content.tex
> > index 835f1ea..47e3566 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -4418,6 +4418,9 @@ \subsection{Feature bits}\label{sec:Device Types
> > / Block Device / Feature bits}
>
> [something seems to have caused line wrapping in this patch]
>
Hmm... I can try applying again and sending out as a v4?
> > \item[VIRTIO_BLK_F_WRITE_ZEROES (14)] Device can support write zeroes
> > command,
> > maximum write zeroes sectors size in \field{max_write_zeroes_sectors}
> > and
> > maximum write zeroes segment number in \field{max_write_zeroes_seg}.
> > +
> > +\item[VIRTIO_BLK_F_LIFETIME (15)] Device supports providing storage
> > lifetime
> > + information.
> > \end{description}
> >
> > \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types
> > / Block Device / Feature bits / Legacy Interface: Feature bits}
> > @@ -4601,14 +4604,16 @@ \subsection{Device Operation}\label{sec:Device
> > Types / Block Device / Device Ope
> >
> > The type of the request is either a read (VIRTIO_BLK_T_IN), a write
> > (VIRTIO_BLK_T_OUT), a discard (VIRTIO_BLK_T_DISCARD), a write zeroes
> > -(VIRTIO_BLK_T_WRITE_ZEROES), a flush (VIRTIO_BLK_T_FLUSH), or a get device
> > ID
> > -string command (VIRTIO_BLK_T_GET_ID).
> > +(VIRTIO_BLK_T_WRITE_ZEROES), a flush (VIRTIO_BLK_T_FLUSH), a get device ID
> > +string command (VIRTIO_BLK_T_GET_ID), or a get device lifetime
> > +command (VIRTIO_BLK_T_GET_LIFETIME).
> >
> > \begin{lstlisting}
> > #define VIRTIO_BLK_T_IN 0
> > #define VIRTIO_BLK_T_OUT 1
> > #define VIRTIO_BLK_T_FLUSH 4
> > #define VIRTIO_BLK_T_GET_ID 8
> > +#define VIRTIO_BLK_T_GET_LIFETIME 10
> > #define VIRTIO_BLK_T_DISCARD 11
> > #define VIRTIO_BLK_T_WRITE_ZEROES 13
> > \end{lstlisting}
> > @@ -4648,6 +4653,23 @@ \subsection{Device Operation}\label{sec:Device
> > Types / Block Device / Device Ope
> > \field{data}. The device ID string is a NUL-padded ASCII string up to 20
> > bytes
> > long. If the string is 20 bytes long then there is no NUL terminator.
> >
> > +The \field{data} used for VIRTIO_BLK_T_GET_LIFETIME requests is populated
> > by
> > +the device, and is of the form:
> > +
> > +\begin{lstlisting}
> > +struct virtio_blk_lifetime {
> > + le16 pre_eol_info;
> > + le16 device_lifetime_est_a;
> > + le16 device_lifetime_est_b;
> > +};
> > +\end{lstlisting}
> > +
> > +The device lifetime metrics \field{pre_eol_info},
> > \field{device_lifetime_est_a}
> > +and \field{device_lifetime_est_b} have the semantics described by the JEDEC
> > +standard No.84-B50 for the extended CSD register fields
> > \field{PRE_EOL_INFO}
> > +\field{DEVICE_LIFETIME_EST_TYP_A} and \field{DEVICE_LIFETIME_EST_TYP_B}
> > +respectively.
>
> Do we have an explicit link to that JEDEC standard?
>
I believe the specification is under a JEDEC paywall. I have access to
it by means of my employer, but it doesn't seem to be publicly
available.
> > +
> > The final \field{status} byte is written by the device: either
> > VIRTIO_BLK_S_OK for success, VIRTIO_BLK_S_IOERR for device or driver
> > error or VIRTIO_BLK_S_UNSUPP for a request unsupported by device:
> > @@ -4754,6 +4776,11 @@ \subsection{Device Operation}\label{sec:Device
> > Types / Block Device / Device Ope
> > (case~\ref{item:flush3}). Failure to do so can cause data loss
> > in case of a crash.
> >
> > +If the device is backed by eMMC or UFS persistent storage, the device
> > SHOULD
> > +offer the VIRTIO_BLK_F_LIFETIME flag. The flag MUST NOT be offered if
> > the device
> > +is backed by storage for which the lifetime metrics as described in
> > this document
> > +cannot be obtained or have no useful meaning.
>
> Isn't that outside of the normative sections? If so, please make this a
> description without SHOULD and MUST NOT, and add them to the normative
> clauses.
>
Hmm.. when I look at my local copy, I see this section right below the clause:
"If the device is backed by persistent storage, the device MUST ensure that
stable writes are committed to it, before reporting completion of the write
(cases~\ref{item:flush1} and~\ref{item:flush2}) or the flush
(case~\ref{item:flush3}). Failure to do so can cause data loss
in case of a crash."
It looked like the right place to add this kind of clause to me, but
if I am wrong and you would like to see it moved, please do let me
know.
Maybe I really do just need to apply the patch again on a clean-slate
repository, if what I see locally does not align?
> Also, are eMMC/UFS just examples (i.e. may other types of persistent
> storage provide these metrics as well?)
>
I can't say I know of other hardware that provides identical metrics,
but it could be possible and maybe could be done by software
adaptation for other storage systems?
> > +
> > If the driver changes \field{writeback} between the submission of the write
> > and its completion, the write could be either volatile or stable when
> > its completion is reported; in other words, the exact behavior is
> > undefined.
>
>
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