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It isn't difficult to determine how big the file will be simply based on the number of emails written to it. We can avoid a roundtrip to the kernel to get the length using lseek by just doing our own book-keeping.
The order that files are read from a directory is arbitrary, so the only way to ensure that the mail is actually listed in chronological order in the journal is to sort it in place after reading all the mail. Sorting the file names lexicographically is enough to also achieve chronological ordering because the timestamps come first, then pids, and then sequence numbers and the fixed length encoding means that correponding place values for each are always compared.
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The
init_journalprogram recreates the journal every time it is run. It does this by reading all the mail files from the mail folder and putting them into a new file and then atomically swapping that file for the old one.Unfortunately the order that dirents are retrieved from a folder is not deterministic so the order that the email ends up in the journal can vary from one run to the next (especially if new items are added).
This interacts poorly with the assumption that access restriction can consist of just limiting the maximum extant of the journal file that a given user can access because the email will appear within the journal chronologically.
In order to fix this issue, a temporary solution is just to sort all the emails within the journal as the file names will lexicographically sort into the appropriate chronological order.
Fixes: #133