posix, windows: introduce cachestat
This class contains a stat result, and possibly other file info to reliably
determine between two points in time whether a file has changed.
Uniquely identifying a file gives us that reliability because we either
atomic rename or append. So one of two will happen: the file 'id' will change,
or the size of the file will change.
posix implements it simply by calling os.stat() and checking if the result
has st_ino.
For now on Windows we always assume the path is uncacheable. This can be
improved on NTFS due to file IDs: http://msdn.microsoft.com/en-us/library/
aa363788(v=vs.85).aspx
So we need to find out if a file path is on an NTFS drive, for that we have:
- GetVolumeInformation, which unfortunately only works with a root path (but is available on XP)
- GetVolumeInformationByHandleW, works on a full file path but requires Vista or higher
$ hg init t
$ cd t
$ echo foo > a
$ hg add a
$ hg commit -m "1"
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
$ chmod -r .hg/store/data/a.i
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
abort: Permission denied: $TESTTMP/t/.hg/store/data/a.i
[255]
$ chmod +r .hg/store/data/a.i
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
$ chmod -w .hg/store/data/a.i
$ echo barber > a
$ hg commit -m "2"
trouble committing a!
abort: Permission denied: $TESTTMP/t/.hg/store/data/a.i
[255]
$ chmod -w .
$ hg diff --nodates
diff -r 2a18120dc1c9 a
--- a/a
+++ b/a
@@ -1,1 +1,1 @@
-foo
+barber
$ chmod +w .
$ chmod +w .hg/store/data/a.i
$ mkdir dir
$ touch dir/a
$ hg status
M a
? dir/a
$ chmod -rx dir
$ hg status
dir: Permission denied
M a
Reenable perm to allow deletion:
$ chmod +rx dir