Fix potential swap undercount on FreeBSD

[jheanlee]

Fixes potential totalSwap and usedSwap undercount on FreeBSD.

The original implementation only reads ARRAYSIZE(swap) - 1 (15) swap devices into the buffer and sum them as totalSwap and usedSwap. If a system has more than 16 devices, the original implementation would not count the remaining devices beyond 16 (maxswap = LEN = 16; kvm_getswapinfo() reads up to maxswap - 1 devices.).

kvm_getswapinfo() reserves the last structure for a total sum of all devices, including those that are not written into the array:

A grand total of all swap devices (including any devices that go beyond maxswap - 1) is returned in one additional array entry.

The grand total is calculated from all available swap devices whether or not you made room for them all in the array.

When maxswap = 1, we get the grand total of all swap devices in the supplied kvm_swap structure.

For proof and more information, please check GuillaumeGomez/sysinfo#1746.

[coderabbitai]

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• freebsd/FreeBSDMachine.c

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📝 Walkthrough

Walkthrough

FreeBSD swap reporting now uses one kvm_getswapinfo() call to obtain the grand total. If the call returns a negative count, the code sets total and used swap to zero. Otherwise, it converts the returned totals from pages to kilobytes.

Suggested reviewers: prownd

Priority: ⬇️ Low

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 1ec61

The change targets accurate FreeBSD swap totals, and the supplied evidence identifies no remaining actionable merge risk.

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_{One call gathers swap totals
A grand total replaces the sum
Negative counts set values to zero
Page totals become kilobytes
FreeBSD reports the result in turn}

_{Comment @coderabbitai help to get the list of available commands.}

[jheanlee]

Would the bug label fit this PR more than enhancement here? This PR fixes the issue that totalSwap and usedSwap are undercounted when there are more than 15 swap devices.