Reformulate sparseWriter #21797
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Reformulate sparseWriter #21797
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- Add more test cases - Test that we create the expected (large) holes; don't enforce anything for the <zerosThresholt ones. O)nly changes test code, should not change behavior. Signed-off-by: Miloslav Trmač <[email protected]>
... instead of using a multi-variable state machine. The net effect of this code is exactly the same as the previous implementation, except: - the operation after Write() returns an error might differ - If the file ends with zeroes, we don't Seek(-1), and we don't create a hole at all if it is too small, preferring to save a syscall. But this formulation is hopefully easier to prove correct. Signed-off-by: Miloslav Trmač <[email protected]>
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Cockpit tests failed for commit 5d303ca. @martinpitt, @jelly, @mvollmer please check. |
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Instead of using a state machine, use a more straight-line code; also document and enforce various invariants.
The net effect of this code is exactly the same as the previous implementation, except:
Seek(-1), and we don't create a hole at all if it is too small, preferring to save a syscall.But this formulation is hopefully easier to prove correct.
Also adds more tests, to see behavior in more cases, and to actually test that this does create holes.
Alternatively, see https://github.com/mtrmac/libpod/tree/sparse for a commit series that ends with exactly the same code, but justifies every step individually.
But in this case I think it’s easier to just read the end product with its comments than to follow the 33 steps one by one.
Does this PR introduce a user-facing change?