[tor-bugs] #26740 [Core Tor/sbws]: Make sbws generate bandwidth files atomically, and document (was: Document that bandwidth files should be generated atomically)

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#26740: Make sbws generate bandwidth files atomically, and document
---------------------------+-------------------------------------
 Reporter:  juga           |          Owner:  teor
     Type:  defect         |         Status:  needs_review
 Priority:  Medium         |      Milestone:  sbws 1.0 (MVP must)
Component:  Core Tor/sbws  |        Version:
 Severity:  Normal         |     Resolution:
 Keywords:                 |  Actual Points:
Parent ID:  #26851         |         Points:
 Reviewer:                 |        Sponsor:
---------------------------+-------------------------------------
Changes (by teor):

 * status:  assigned => needs_review
 * milestone:  sbws 1.0 (MVP nice) => sbws 1.0 (MVP must)


Comment:

 sbws was deleting the symlink after generating the file. When the symlink
 is deleted, reading the path is not atomic, because it can fail with a
 file not found error.

 This change is based on nickm's feedback at:
 https://trac.torproject.org/projects/tor/ticket/26702#comment:12

 Please see my pull request:
 https://github.com/pastly/simple-bw-scanner/pull/237

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26740#comment:15>
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