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Subject: Re: [virtio-dev] [PATCH v3] Add lifetime metrics to virtio-blk
On Mon, 1 Mar 2021 10:51:03 -0700 Enrico Granata <egranata@google.com> 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 <egranata@google.com> > --- > 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] > \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? > + > 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. Also, are eMMC/UFS just examples (i.e. may other types of persistent storage provide these metrics as well?) > + > 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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