Merge ChangeSet@1.10: Documentation about flist scalabilityTODO

[rsync/rsync.git] / TODO

-*- indented-text -*-

URGENT ---------------------------------------------------------------


IMPORTANT ------------------------------------------------------------

Cross-test versions

  Part of the regression suite should be making sure that we don't
  break backwards compatibility: old clients vs new servers and so
  on.  Ideally we would test the cross product of versions.  

  It might be sufficient to test downloads from well-known public
  rsync servers running different versions of rsync.  This will give
  some testing and also be the most common case for having different
  versions and not being able to upgrade.

use chroot

  If the platform doesn't support it, then don't even try.

  If running as non-root, then don't fail, just give a warning.
  (There was a thread about this a while ago?)

    http://lists.samba.org/pipermail/rsync/2001-August/thread.html
    http://lists.samba.org/pipermail/rsync/2001-September/thread.html

--files-from

  Avoids traversal.  Better option than a pile of --include statements
  for people who want to generate the file list using a find(1)
  command or a script.

Performance

  Traverse just one directory at a time.  Tridge says it's possible.

  At the moment rsync reads the whole file list into memory at the
  start, which makes us use a lot of memory and also not pipeline
  network access as much as we could.

  We need to be careful of duplicate names getting into the file list.
  See clean_flist().  This could happen if multiple arguments include
  the same file.  Bad.

  I think duplicates are only a problem if they're both flowing
  through the pipeline at the same time.  For example we might have
  updated the first occurrence after reading the checksums for the
  second.  So possibly we just need to make sure that we don't have
  both in the pipeline at the same time.  

  Possibly if we did one directory at a time that would be sufficient.

  Alternatively we could pre-process the arguments to make sure no
  duplicates will ever be inserted.  There could be some bad cases
  when we're collapsing symlinks.

  We could have a hash table.

  The root of the problem is that we do not want more than one file
  list entry referring to the same file.  At first glance there are
  several ways this could happen: symlinks, hardlinks, and repeated
  names on the command line.

  If names are repeated on the command line, they may be present in
  different forms, perhaps by traversing directory paths in different
  ways, traversing paths including symlinks.  Also we need to allow
  for expansion of globs by rsync.

  At the moment, clean_flist() requires having the entire file list in
  memory.  Duplicate names are detected just by a string comparison.

  We don't need to worry about hard links causing duplicates because
  files are never updated in place.  Similarly for symlinks.

  I think even if we're using a different symlink mode we don't need
  to worry.

Memory accounting

  At exit, show how much memory was used for the file list, etc.

  Also we do a wierd exponential-growth allocation in flist.c.  I'm
  not sure this makes sense with modern mallocs.  At any rate it will
  make us allocate a huge amount of memory for large file lists.

Hard-link handling

  At the moment hardlink handling is very expensive, so it's off by
  default.  It does not need to be so.  

  We can rule out hardlinked directories since they will probably
  screw us up in all kinds of ways.  They simply should not be used.

  At the moment rsync only cares about hardlinks to regular files.  I
  guess you could also use them for sockets, devices and other beasts,
  but I have not seen them.

  When trying to reproduce hard links, we only need to worry about
  files that have more than one name (nlinks>1 && !S_ISDIR). 

  The basic point of this is to discover alternate names that refer to
  the same file.  All operations, including creating the file and
  writing modifications to it need only to be done for the first name.
  For all later names, we just create the link and then leave it
  alone.

  If hard links are to be preserved:

    Before the generator/receiver fork, the list of files is received
    from the sender (recv_file_list), and a table for detecting hard
    links is built.

    The generator looks for hard links within the file list and does
    not send checksums for them, though it does send other metadata.

    The sender sends the device number and inode with file entries, so
    that files are uniquely identified.

    The receiver goes through and creates hard links (do_hard_links)
    after all data has been written, but before directory permissions
    are set.

  At the moment device and inum are sent as 4-byte integers, which
  will probably cause problems on large filesystems.  On Linux the
  kernel uses 64-bit ino_t's internally, and people will soon have
  filesystems big enough to use them.  We ought to follow NFS4 in
  using 64-bit device and inode identification, perhaps with a
  protocol version bump.

  Once we've seen all the names for a particular file, we no longer
  need to think about it and we can deallocate the memory.

  We can also have the case where there are links to a file that are
  not in the tree being transferred.  There's nothing we can do about
  that.  Because we rename the destination into place after writing,
  any hardlinks to the old file are always going to be orphaned.  In
  fact that is almost necessary because otherwise we'd get really
  confused if we were generating checksums for one name of a file and
  modifying another.

  At the moment the code seems to make a whole second copy of the file
  list, which seems unnecessary.

  We should have a test case that exercises hard links.  Since it
  might be hard to compare ./tls output where the inodes change we
  might need a little program to check whether several names refer to
  the same file.

IPv6

  Implement suggestions from http://www.kame.net/newsletter/19980604/
  and ftp://ftp.iij.ad.jp/pub/RFC/rfc2553.txt

  If a host has multiple addresses, then listen try to connect to all
  in order until we get through.  (getaddrinfo may return multiple
  addresses.)  This is kind of implemented already.

  Possibly also when starting as a server we may need to listen on
  multiple passive addresses.  This might be a bit harder, because we
  may need to select on all of them.  Hm.

  Define a syntax for IPv6 literal addresses.  Since they include
  colons, they tend to break most naming systems, including ours.
  Based on the HTTP IPv6 syntax, I think we should use
 
     rsync://[::1]/foo/bar
     [::1]::bar

  which should just take a small change to the parser code.

Errors

  If we hang or get SIGINT, then explain where we were up to.  Perhaps
  have a static buffer that contains the current function name, or
  some kind of description of what we were trying to do.  This is a
  little easier on people than needing to run strace/truss.

  "The dungeon collapses!  You are killed."  Rather than "unexpected
  eof" give a message that is more detailed if possible and also more
  helpful.  

File attributes

  Device major/minor numbers should be at least 32 bits each.  See
  http://lists.samba.org/pipermail/rsync/2001-November/005357.html

  Transfer ACLs.  Need to think of a standard representation.
  Probably better not to even try to convert between NT and POSIX.
  Possibly can share some code with Samba.

Empty directories

  With the current common --include '*/' --exclude '*' pattern, people
  can end up with many empty directories.  We might avoid this by
  lazily creating such directories.

zlib

  Perhaps don't use our own zlib.  Will we actually be incompatible,
  or just be slightly less efficient?

logging

  Perhaps flush stdout after each filename, so that people trying to
  monitor progress in a log file can do so more easily.  See
  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=48108

rsyncd over ssh

  There are already some patches to do this.

PLATFORMS ------------------------------------------------------------

Win32

  Don't detach, because this messes up --srvany.

  http://sources.redhat.com/ml/cygwin/2001-08/msg00234.html

  According to "Effective TCP/IP Programming" (??) close() on a socket
  has incorrect behaviour on Windows -- it sends a RST packet to the
  other side, which gives a "connection reset by peer" error.  On that
  platform we should probably do shutdown() instead.  However, on Unix
  we are correct to call close(), because shutdown() discards
  untransmitted data.

DOCUMENTATION --------------------------------------------------------

Update README

BUILD FARM -----------------------------------------------------------

Add machines

  AMDAHL UTS (Dave Dykstra)

  Cygwin (on different versions of Win32?)

  HP-UX variants (via HP?)

  SCO

NICE -----------------------------------------------------------------

SIGHUP

  Re-read config file (just exec() ourselves) rather than exiting.

--no-detach and --no-fork options

  Very useful for debugging.  Also good when running under a
  daemon-monitoring process that tries to restart the service when the
  parent exits.

hang/timeout friendliness

verbose output
  
  Indicate whether files are new, updated, or deleted

internationalization

  Change to using gettext().  Probably need to ship this for platforms
  that don't have it.  

  Solicit translations.

  Does anyone care?

rsyncsh 

   Write a small emulation of interactive ftp as a Pythonn program
   that calls rsync.  Commands such as "cd", "ls", "ls *.c" etc map
   fairly directly into rsync commands: it just needs to remember the
   current host, directory and so on.  We can probably even do
   completion of remote filenames.

%K%