[arista] Limit eeprom reads to 512 bytes

[dzarista]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

Summary

Currently, when reading eeproms, the entire memory space is read, which can take a lot of time. This PR proposes reducing reads to a maximum of 512 bytes. The primary motivation is to reduce platform manager initialization time as well as weutil time.

ParserUtils::loadEeprom() is changed to read a fixed 512-byte region instead of the full file, and IoctlSmbusEepromReader::readEeprom() is updated to accept a length parameter capped at the same limit.

Test Plan

Build passes.
sw_tests pass
weutil_hw_test and platform_manager_hw_test passes across arista platforms
platform_manager reload time reduced by 15-20 seconds across arista platforms

[meta-codesync]

@somasun has imported this pull request. If you are a Meta employee, you can view this in D96379392.

[somasun]

@dzarista - how much improvement are you seeing in platform set up time with this change?

[somasun]

platform_manager reload time reduced by 15-20 seconds across arista platforms

nevermind. I see "platform_manager reload time reduced by 15-20 seconds across arista platforms"

[somasun]

Can you add test coverage for this new 512-byte limit

[somasun]

@dzarista - any update on the PR ?

[facebook-github-tools]

@dzarista has updated the pull request. You must reimport the pull request before landing.

[dzarista]

@dzarista - any update on the PR ?

@somasun, apologies for the delay, I've addressed your comments. Regarding testing, I ended up adding a new test file ParserUtilsTest.cpp, which specifically tests that only 512 bytes were read. I opted not to put this in FbossEepromInterfaceTest.cpp as I found it difficult to work it in to that file's format which works with eeproms that are less than 512 bytes.

The test gets built as weuitl_parser_utils_test, and I tested that it passed.