--- a/hgext/lfs/__init__.py	Tue Oct 09 21:53:21 2018 -0400
+++ b/hgext/lfs/__init__.py	Thu Oct 04 00:17:26 2018 -0400
@@ -124,6 +124,8 @@
 
 from __future__ import absolute_import
 
+import sys
+
 from mercurial.i18n import _
 
 from mercurial import (
@@ -204,6 +206,12 @@
 templatekeyword = registrar.templatekeyword()
 filesetpredicate = registrar.filesetpredicate()
 
+lfsprocessor = (
+    wrapper.readfromstore,
+    wrapper.writetostore,
+    wrapper.bypasscheckhash,
+)
+
 def featuresetup(ui, supported):
     # don't die on seeing a repo with the lfs requirement
     supported |= {'lfs'}
@@ -302,12 +310,28 @@
     wrapfunction(filelog, 'renamed', wrapper.filelogrenamed)
     wrapfunction(filelog, 'size', wrapper.filelogsize)
 
+def _resolverevlogstorevfsoptions(orig, ui, requirements, features):
+    opts = orig(ui, requirements, features)
+    for name, module in extensions.extensions(ui):
+        if module is sys.modules[__name__]:
+            if revlog.REVIDX_EXTSTORED in opts[b'flagprocessors']:
+                msg = (_(b"cannot register multiple processors on flag '%#x'.")
+                       % revlog.REVIDX_EXTSTORED)
+                raise error.Abort(msg)
+
+            opts[b'flagprocessors'][revlog.REVIDX_EXTSTORED] = lfsprocessor
+            break
+
+    return opts
+
 def extsetup(ui):
     wrapfilelog(filelog.filelog)
 
     wrapfunction = extensions.wrapfunction
 
     wrapfunction(localrepo, 'makefilestorage', wrapper.localrepomakefilestorage)
+    wrapfunction(localrepo, 'resolverevlogstorevfsoptions',
+                 _resolverevlogstorevfsoptions)
 
     wrapfunction(cmdutil, '_updatecatformatter', wrapper._updatecatformatter)
     wrapfunction(scmutil, 'wrapconvertsink', wrapper.convertsink)
@@ -334,15 +358,6 @@
     wrapfunction(context.basefilectx, 'isbinary', wrapper.filectxisbinary)
     context.basefilectx.islfs = wrapper.filectxislfs
 
-    revlog.addflagprocessor(
-        revlog.REVIDX_EXTSTORED,
-        (
-            wrapper.readfromstore,
-            wrapper.writetostore,
-            wrapper.bypasscheckhash,
-        ),
-    )
-
     scmutil.fileprefetchhooks.add('lfs', wrapper._prefetchfiles)
 
     # Make bundle choose changegroup3 instead of changegroup2. This affects

--- a/tests/test-lfs-serve.t	Tue Oct 09 21:53:21 2018 -0400
+++ b/tests/test-lfs-serve.t	Thu Oct 04 00:17:26 2018 -0400
@@ -35,6 +35,26 @@
   $ hg init server
   $ SERVER_REQUIRES="$TESTTMP/server/.hg/requires"
 
+  $ cat > $TESTTMP/debugprocessors.py <<EOF
+  > from mercurial import (
+  >     cmdutil,
+  >     commands,
+  >     pycompat,
+  >     registrar,
+  > )
+  > cmdtable = {}
+  > command = registrar.command(cmdtable)
+  > @command(b'debugprocessors', [], b'FILE')
+  > def debugprocessors(ui, repo, file_=None, **opts):
+  >     opts = pycompat.byteskwargs(opts)
+  >     opts[b'changelog'] = False
+  >     opts[b'manifest'] = False
+  >     opts[b'dir'] = False
+  >     rl = cmdutil.openrevlog(repo, b'debugprocessors', file_, opts)
+  >     for flag, proc in rl._flagprocessors.iteritems():
+  >         ui.status(b"registered processor '%#x'\n" % (flag))
+  > EOF
+
 Skip the experimental.changegroup3=True config.  Failure to agree on this comes
 first, and causes a "ValueError: no common changegroup version" or "abort:
 HTTP Error 500: Internal Server Error", if the extension is only loaded on one
@@ -42,6 +62,8 @@
 for flag '0x2000'!" if the extension is only loaded on one side (possibly also
 masked by the Internal Server Error message).
   $ cat >> $HGRCPATH <<EOF
+  > [extensions]
+  > debugprocessors = $TESTTMP/debugprocessors.py
   > [experimental]
   > lfs.disableusercache = True
   > [lfs]
@@ -51,6 +73,8 @@
   > push_ssl=False
   > EOF
 
+  $ cp $HGRCPATH $HGRCPATH.orig
+
 #if lfsremote-on
   $ hg --config extensions.lfs= -R server \
   >    serve -p $HGPORT -d --pid-file=hg.pid --errorlog=$TESTTMP/errors.log
@@ -307,6 +331,103 @@
   $ hg identify http://localhost:$HGPORT
   c729025cc5e3
 
+  $ mv $HGRCPATH $HGRCPATH.tmp
+  $ cp $HGRCPATH.orig $HGRCPATH
+
+  >>> from __future__ import absolute_import
+  >>> from hgclient import check, readchannel, runcommand
+  >>> @check
+  ... def checkflags(server):
+  ...     readchannel(server)
+  ...     print('')
+  ...     print('# LFS required- both lfs and non-lfs revlogs have 0x2000 flag')
+  ...     runcommand(server, ['debugprocessors', 'lfs.bin', '-R',
+  ...                '../server'])
+  ...     runcommand(server, ['debugprocessors', 'nonlfs2.txt', '-R',
+  ...                '../server'])
+  ...     runcommand(server, ['config', 'extensions', '--cwd',
+  ...                '../server'])
+  ... 
+  ...     print("\n# LFS not enabled- revlogs don't have 0x2000 flag")
+  ...     runcommand(server, ['debugprocessors', 'nonlfs3.txt'])
+  ...     runcommand(server, ['config', 'extensions'])
+  
+  # LFS required- both lfs and non-lfs revlogs have 0x2000 flag
+  *** runcommand debugprocessors lfs.bin -R ../server
+  registered processor '0x8000'
+  registered processor '0x2000'
+  *** runcommand debugprocessors nonlfs2.txt -R ../server
+  registered processor '0x8000'
+  registered processor '0x2000'
+  *** runcommand config extensions --cwd ../server
+  extensions.debugprocessors=$TESTTMP/debugprocessors.py
+  extensions.lfs=
+  
+  # LFS not enabled- revlogs don't have 0x2000 flag
+  *** runcommand debugprocessors nonlfs3.txt
+  registered processor '0x8000'
+  *** runcommand config extensions
+  extensions.debugprocessors=$TESTTMP/debugprocessors.py
+
+  $ rm $HGRCPATH
+  $ mv $HGRCPATH.tmp $HGRCPATH
+
+  $ hg clone $TESTTMP/client $TESTTMP/nonlfs -qr 0 --config extensions.lfs=
+  $ cat >> $TESTTMP/nonlfs/.hg/hgrc <<EOF
+  > [extensions]
+  > lfs = !
+  > EOF
+
+  >>> from __future__ import absolute_import, print_function
+  >>> from hgclient import check, readchannel, runcommand
+  >>> @check
+  ... def checkflags2(server):
+  ...     readchannel(server)
+  ...     print('')
+  ...     print('# LFS enabled- both lfs and non-lfs revlogs have 0x2000 flag')
+  ...     runcommand(server, ['debugprocessors', 'lfs.bin', '-R',
+  ...                '../server'])
+  ...     runcommand(server, ['debugprocessors', 'nonlfs2.txt', '-R',
+  ...                '../server'])
+  ...     runcommand(server, ['config', 'extensions', '--cwd',
+  ...                '../server'])
+  ... 
+  ...     print('\n# LFS enabled without requirement- revlogs have 0x2000 flag')
+  ...     runcommand(server, ['debugprocessors', 'nonlfs3.txt'])
+  ...     runcommand(server, ['config', 'extensions'])
+  ... 
+  ...     print("\n# LFS disabled locally- revlogs don't have 0x2000 flag")
+  ...     runcommand(server, ['debugprocessors', 'nonlfs.txt', '-R',
+  ...                '../nonlfs'])
+  ...     runcommand(server, ['config', 'extensions', '--cwd',
+  ...                '../nonlfs'])
+  
+  # LFS enabled- both lfs and non-lfs revlogs have 0x2000 flag
+  *** runcommand debugprocessors lfs.bin -R ../server
+  registered processor '0x8000'
+  registered processor '0x2000'
+  *** runcommand debugprocessors nonlfs2.txt -R ../server
+  registered processor '0x8000'
+  registered processor '0x2000'
+  *** runcommand config extensions --cwd ../server
+  extensions.debugprocessors=$TESTTMP/debugprocessors.py
+  extensions.lfs=
+  
+  # LFS enabled without requirement- revlogs have 0x2000 flag
+  *** runcommand debugprocessors nonlfs3.txt
+  registered processor '0x8000'
+  registered processor '0x2000'
+  *** runcommand config extensions
+  extensions.debugprocessors=$TESTTMP/debugprocessors.py
+  extensions.lfs=
+  
+  # LFS disabled locally- revlogs don't have 0x2000 flag
+  *** runcommand debugprocessors nonlfs.txt -R ../nonlfs
+  registered processor '0x8000'
+  *** runcommand config extensions --cwd ../nonlfs
+  extensions.debugprocessors=$TESTTMP/debugprocessors.py
+  extensions.lfs=!
+
 --------------------------------------------------------------------------------
 Case #6: client with lfs content and the extension enabled; server with
 lfs content, and the extension enabled.