1 /*
2 // Copyright (c) 2022 Equinix, Inc.
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 // http://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15 */
16
17 #include "fru_reader.hpp"
18
19 #include <cstring>
20
read(off_t start,size_t len,uint8_t * outbuf)21 ssize_t FRUReader::read(off_t start, size_t len, uint8_t* outbuf)
22 {
23 size_t done = 0;
24 size_t remaining = len;
25 size_t cursor = start;
26 while (done < len)
27 {
28 if (eof.has_value() && cursor >= eof.value())
29 {
30 break;
31 }
32
33 const uint8_t* blkData = nullptr;
34 size_t available = 0;
35 size_t blk = cursor / cacheBlockSize;
36 size_t blkOffset = cursor % cacheBlockSize;
37 auto findBlk = cache.find(blk);
38 if (findBlk == cache.end())
39 {
40 // miss, populate cache
41 uint8_t* newData = cache[blk].data();
42 int64_t ret = readFunc(blk * cacheBlockSize, cacheBlockSize,
43 newData);
44
45 // if we've reached the end of the eeprom, record its size
46 if (ret >= 0 && static_cast<size_t>(ret) < cacheBlockSize)
47 {
48 eof = (blk * cacheBlockSize) + ret;
49 }
50
51 if (ret <= 0)
52 {
53 // don't leave empty blocks in the cache
54 cache.erase(blk);
55 return done != 0U ? done : ret;
56 }
57
58 blkData = newData;
59 available = ret;
60 }
61 else
62 {
63 // hit, use cached data
64 blkData = findBlk->second.data();
65
66 // if the hit is to the block containing the (previously
67 // discovered on the miss that populated it) end of the eeprom,
68 // don't copy spurious bytes past the end
69 if (eof.has_value() && (eof.value() / cacheBlockSize == blk))
70 {
71 available = eof.value() % cacheBlockSize;
72 }
73 else
74 {
75 available = cacheBlockSize;
76 }
77 }
78
79 size_t toCopy = (blkOffset >= available)
80 ? 0
81 : std::min(available - blkOffset, remaining);
82
83 // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-pointer-arithmetic)
84 memcpy(outbuf + done, blkData + blkOffset, toCopy);
85 cursor += toCopy;
86 done += toCopy;
87 remaining -= toCopy;
88 }
89
90 return done;
91 }
92