safe_create_leading_directories(): add new error value SCLD_VANISHED
Add a new possible error result that can be returned by safe_create_leading_directories() and safe_create_leading_directories_const(): SCLD_VANISHED. This value indicates that a file or directory on the path existed at one point (either it already existed or the function created it), but then it disappeared. This probably indicates that another process deleted the directory while we were working. If SCLD_VANISHED is returned, the caller might want to retry the function call, as there is a chance that a new attempt will succeed. Why doesn't safe_create_leading_directories() do the retrying internally? Because an empty directory isn't really ever safe until it holds a file. So even if safe_create_leading_directories() were absolutely sure that the directory existed before it returned, there would be no guarantee that the directory still existed when the caller tried to write something in it. Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
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