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happiness, as well as correct other bugs: - Replace notion of current and saved accounting credential/vnode with a single credential/vnode and an acct_suspended flag. This simplifies the accounting logic substantially. - Replace acct_mtx with acct_sx, a sleepable lock held exclusively during reconfiguration and space polling, but shared during log entry generation. This avoids holding a mutex over sleepable VFS operations. - Hold the sx lock over the duration of the I/O so that the vnode I/O cannot occur after vnode close, which could occur previously if accounting was disabled as a process exited. - Write the accounting log entry with Giant conditionally acquired based on the file system where the log is stored. Previously, the accounting code relied on the caller acquiring Giant. - Acquire Giant conditionally in the accounting callout based on the file system where the accounting log is stored. Run the callout MPSAFE. - Expose acct_suspended via a read-only sysctl so it is possibly to programmatically determine whether accounting is suspended or not without attempting to parse logs. - Check both acct_vp and acct_suspended lock-free before entering the accounting sx lock in acct(). - When accounting is disabled due to a VBAD vnode (i.e., forceable unmount), generate a log message indicating accounting has been disabled. - Correct a long-standing bug in how free space is calculated and compared to the required space: generate and compare signed results, not unsigned results, or negative free space will cause accounting to not be suspended when required, or worse, incorrectly resumed once negative free space is reached. MFC after: 2 weeks
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