nodemap: update the index with the newly written data (when appropriate) If we are to use mmap to read the nodemap data, and if the python code is responsible for the IO, we need to refresh the mmap after each write and provide it back to the index. We start this dance without the mmap first. Differential Revision: https://phab.mercurial-scm.org/D7893

nodemap: never read more than the expected data amount Since we are tracking this number we can use it to detect corrupted rawdata file and to only read the correct amount of data when possible. Differential Revision: https://phab.mercurial-scm.org/D7892

nodemap: write new data from the expected current data length If the amount of data in the file exceed the expect amount, we will overwrite the extra data. This is a simple way to be safer. Differential Revision: https://phab.mercurial-scm.org/D7891

nodemap: double check the source docket when doing incremental update In theory, the index will have the information we expect it to have. However by security, it seems safer to double check that the incremental data are generated from the data currently on disk. Differential Revision: https://phab.mercurial-scm.org/D7890

nodemap: track the total and unused amount of data in the rawdata file We need to keep that information around: * total data will allow transaction to start appending new information without confusing other reader. * unused data will allow to detect when we should regenerate new rawdata file. Differential Revision: https://phab.mercurial-scm.org/D7889

nodemap: track the maximum revision tracked in the nodemap We need a simple way to detect when the on disk data contains less revision than the index we read from disk. The docket file is meant for this, we just had to start tracking that data. We should also try to detect strip operation, but we will deal with this in later changesets. Right now we are focusing on defining the API for index supporting persistent nodemap. Differential Revision: https://phab.mercurial-scm.org/D7888

nodemap: add a flag to dump the details of the docket We are about to add more information to the docket. We first introduce a way to debug its content. Differential Revision: https://phab.mercurial-scm.org/D7887