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Subject: [PATCH v2] Add lifetime metrics to virtio-blk
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..0e73ff0 100644 --- a/content.tex +++ b/content.tex @@ -4418,6 +4418,9 @@ \subsection{Feature bits}\label{sec:Device Types / Block Device / Feature bits} \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} @@ -4601,8 +4604,9 @@ \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 @@ -4611,6 +4615,7 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope #define VIRTIO_BLK_T_GET_ID 8 #define VIRTIO_BLK_T_DISCARD 11 #define VIRTIO_BLK_T_WRITE_ZEROES 13 +#define VIRTIO_BLK_T_GET_LIFETIME 15 \end{lstlisting} The \field{sector} number indicates the offset (multiplied by 512) where @@ -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. + 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. + 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. -- 2.30.1.766.gb4fecdf3b7-goog
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