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To understand the problem, we need some definitions. The driver is aware of multiple counters (enum ocelot_stat), yet not all switches supported by the driver implement all counters. There are 2 statistics layouts: ocelot_stats_layout and ocelot_mm_stats_layout, the latter having 36 counters more than the former. ocelot->stats[] is not a compact array, i.e. there are elements within it which are not going to be populated for ocelot_stats_layout. On the other hand, ocelot->stats[] is easily indexable, for example "tx_octets" for port 3 can be found at ocelot->stats[3 * OCELOT_NUM_STATS + OCELOT_STAT_TX_OCTETS], and that is why we keep it sparse. Regions, as created by ocelot_prepare_stats_regions(), are compact (every element from region->buf will correspond to a counter that is present in this switch's layout) but are not easily indexable. Let's define holes as the ranges of values of enum ocelot_stat for which ocelot_stats_layout doesn't have a "reg" defined. For example, there is a hole between OCELOT_STAT_RX_GREEN_PRIO_7 and OCELOT_STAT_TX_OCTETS which is of 23 elements that are only present on ocelot_mm_stats_layout, and as such, they are also present in enum ocelot_stat. Let's define the left extremity of the hole - the last enum ocelot_stat still defined - as A (in this case OCELOT_STAT_RX_GREEN_PRIO_7) and the right extremity - the first enum ocelot_stat that is defined after a series of undefined ones - as B (in this case OCELOT_STAT_TX_OCTETS). There is a bug in the procedure which transfers stats from region->buf[] to ocelot->stats[]. For each hole in the ocelot_stats_layout, the logic transfers the stats starting with enum ocelot_stat B to ocelot->stats[] index A + 1. So all stats after a hole are saved to a position which is off by B - A + 1 elements. This causes 2 kinds of issues: (a) counters which shouldn't increment increment (b) counters which should increment don't Holes in the ocelot_stat_layout automatically imply the end of a region and the beginning of a new one; however the reverse is not necessarily true. For example, for ocelot_mm_stat_layout, there could be multiple regions (which indicate discontinuities in register addresses) while there is no hole (which indicates discontinuities in enum ocelot_stat values). In the example above, the stats from the second region->buf[] are not transferred to ocelot->stats starting with index "port * OCELOT_NUM_STATS + OCELOT_STAT_TX_OCTETS" as they should, but rather, starting with element "port * OCELOT_NUM_STATS + OCELOT_STAT_RX_GREEN_PRIO_7 + 1". That stats[] array element is not reported to user space for switches that use ocelot_stat_layout, and that is how issue (b) occurs. However, if the length of the second region is larger than the hole, then some stats will start to be transferred to the ocelot->stats[] indices which *are* reported to user space, but those indices contain wrong values (corresponding to unexpected counters). This is how issue (a) occurs. The procedure, as it was introduced in commit |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.