[LTP] lib: Use backoff polling to wait for loop device nodes

[linuxtestproject.agent@gmail.com]

Hi Wake,

On Aug 7, 2026, Wake Liu wrote:
> lib: Use backoff polling to wait for loop device nodes

> Introduce an exponential-backoff retry loop in both
> tst_find_free_loopdev() and tst_attach_device() (starting at 1ms delay,
> doubling each try, capped at 100ms) to wait for the device node to be
> successfully populated.

Could the timing description be corrected, or the implementation changed to
match it? TST_RETRY_FN_EXP_BACKOFF() starts tst_delay_ at 1 and passes it to
usleep(), so the first delay is 1 microsecond. MAX_DELAY is converted from
seconds to microseconds, so passing 1 retries for about one second before LTP
timeout scaling, not 100 ms.

Verdict - Needs revision

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