From 616eb27b80756b473711c8ebfcff4614322bad41 Mon Sep 17 00:00:00 2001 From: Daira Hopwood Date: Mon, 28 Dec 2015 19:18:28 +0000 Subject: [PATCH] Fix a subtle bug in the overwrite algorithm. See https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2640#comment:3 . Signed-off-by: Daira Hopwood --- .../magic-folder/remote-to-local-sync.rst | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/docs/proposed/magic-folder/remote-to-local-sync.rst b/docs/proposed/magic-folder/remote-to-local-sync.rst index b41de7bf..8854913c 100644 --- a/docs/proposed/magic-folder/remote-to-local-sync.rst +++ b/docs/proposed/magic-folder/remote-to-local-sync.rst @@ -375,7 +375,12 @@ this procedure for an overwrite in response to a remote change: conflict. (This takes as input the ``last_downloaded_uri`` field from the directory entry of the changed ``foo``.) 3. Set the ``mtime`` of the replacement file to be *T* seconds - before the current local time. + before the current local time. Stat the replacement file + to obtain its ``mtime`` and ``ctime`` as stored in the local + filesystem, and update the file's last-seen statinfo in + the magic folder db with this information. (Note that the + retrieved ``mtime`` may differ from the one that was set due + to rounding.) 4. Perform a ''file replacement'' operation (explained below) with backup filename ``foo.backup``, replaced file ``foo``, and replacement file ``.foo.tmp``. If any step of this @@ -409,10 +414,10 @@ set in step 3. The move operation in step 4b will cause a step 4c will cause an ``IN_CREATE`` event for ``foo``. However, these events will not trigger an upload, because they are guaranteed to be processed only after the file replacement -has finished, at which point the metadata recorded in the -database entry will exactly match the metadata for the file's -inode on disk. (The two hard links — ``foo`` and, while it -still exists, ``.foo.tmp`` — share the same inode and +has finished, at which point the last-seen statinfo recorded +in the database entry will exactly match the metadata for the +file's inode on disk. (The two hard links — ``foo`` and, while +it still exists, ``.foo.tmp`` — share the same inode and therefore the same metadata.) .. _`magic folder db`: filesystem_integration.rst#local-scanning-and-database @@ -786,7 +791,7 @@ may be absent). Then the algorithm is: * 2b. Read the following information for the path ``foo`` from the local magic folder db: - * the *last-uploaded statinfo*, if any (this is the size in + * the *last-seen statinfo*, if any (this is the size in bytes, ``mtime``, and ``ctime`` stored in the ``local_files`` table when the file was last uploaded); * the ``last_uploaded_uri`` field of the ``local_files`` table @@ -796,7 +801,7 @@ may be absent). Then the algorithm is: * 2c. If any of the following are true, then classify as a conflict: * i. there are pending notifications of changes to ``foo``; - * ii. the last-uploaded statinfo is either absent (i.e. there is + * ii. the last-seen statinfo is either absent (i.e. there is no entry in the database for this path), or different from the current statinfo; * iii. either ``last_downloaded_uri`` or ``last_uploaded_uri`` -- 2.45.2