fru-device: add FRUReader EEPROM cache
This doesn't provide a huge benefit currently, but is a preparatory step
for adding support for a wider variety of FRU format parsers. If
parsers for multiple formats are interested in reading the same areas of
an EEPROM, the caching provided by this abstraction avoids the redundant
bus traffic of all of them re-reading the same bytes over and over.
Tested: on an ASRock Rack romed8hm3, fru-device successfully recognizes
and parses the baseboard FRU EEPROM as it did prior to this patch.
Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Change-Id: I0d774508bc29dbda346309fe7fe42dbdf97bee43
diff --git a/src/fru_reader.cpp b/src/fru_reader.cpp
new file mode 100644
index 0000000..e381e7e
--- /dev/null
+++ b/src/fru_reader.cpp
@@ -0,0 +1,90 @@
+/*
+// Copyright (c) 2022 Equinix, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+*/
+
+#include "fru_reader.hpp"
+
+#include <cstring>
+
+ssize_t FRUReader::read(off_t start, size_t len, uint8_t* outbuf)
+{
+ size_t done = 0;
+ size_t remaining = len;
+ size_t cursor = start;
+ while (done < len)
+ {
+ if (eof.has_value() && cursor >= eof.value())
+ {
+ break;
+ }
+
+ const uint8_t* blkData;
+ size_t available;
+ size_t blk = cursor / cacheBlockSize;
+ size_t blkOffset = cursor % cacheBlockSize;
+ auto findBlk = cache.find(blk);
+ if (findBlk == cache.end())
+ {
+ // miss, populate cache
+ uint8_t* newData = cache[blk].data();
+ int64_t ret =
+ readFunc(blk * cacheBlockSize, cacheBlockSize, newData);
+
+ // if we've reached the end of the eeprom, record its size
+ if (ret >= 0 && static_cast<size_t>(ret) < cacheBlockSize)
+ {
+ eof = (blk * cacheBlockSize) + ret;
+ }
+
+ if (ret <= 0)
+ {
+ // don't leave empty blocks in the cache
+ cache.erase(blk);
+ return done ? done : ret;
+ }
+
+ blkData = newData;
+ available = ret;
+ }
+ else
+ {
+ // hit, use cached data
+ blkData = findBlk->second.data();
+
+ // if the hit is to the block containing the (previously
+ // discovered on the miss that populated it) end of the eeprom,
+ // don't copy spurious bytes past the end
+ if (eof.has_value() && (eof.value() / cacheBlockSize == blk))
+ {
+ available = eof.value() % cacheBlockSize;
+ }
+ else
+ {
+ available = cacheBlockSize;
+ }
+ }
+
+ size_t toCopy = (blkOffset >= available)
+ ? 0
+ : std::min(available - blkOffset, remaining);
+
+ memcpy(outbuf + done, blkData + blkOffset, toCopy);
+ cursor += toCopy;
+ done += toCopy;
+ remaining -= toCopy;
+ }
+
+ return done;
+}