Re: [PATCH] guix-daemon: Add option to disable garbage collection.

[Roel Janssen <roel@gnu.org>]

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Ludovic Courtès <ludovic.courtes@inria.fr> writes:

> Hello Roel,
>
> Roel Janssen <roel@gnu.org> skribis:
>

[...]

>
>> From 00f489d6303720c65571fdf0bc9ee810a20f70e0 Mon Sep 17 00:00:00 2001
>> From: Roel Janssen <roel@gnu.org>
>> Date: Wed, 11 Apr 2018 09:52:11 +0200
>> Subject: [PATCH] guix-daemon: Disable garbage collection for remote hosts.
>>
>> * nix/libstore/gc.cc (collectGarbage): Check for remote connections.
>> * nix/libstore/globals.hh: Add isRemoteConnection setting.
>> * nix/nix-daemon/nix-daemon.cc (performOp): Display appropriate error message;
>>   (acceptConnection): Set isRemoteConnection when connection is over TCP.
>
> [...]
>
>> --- a/nix/libstore/gc.cc
>> +++ b/nix/libstore/gc.cc
>> @@ -595,6 +595,10 @@ void LocalStore::removeUnusedLinks(const GCState & state)
>>  
>>  void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
>>  {
>> +    if (settings.isRemoteConnection) {
>> +        return;
>> +    }
>
> I think this is unnecessary since the daemon already checks for that.
> (It’s also nicer to keep ‘LocalStore’ unaware of the connection
> details.)

Right.  It is indeed unnecessary.  In the updated patch, I no longer do this.

>
>> diff --git a/nix/nix-daemon/nix-daemon.cc b/nix/nix-daemon/nix-daemon.cc
>> index deb7003d7..65770ba95 100644
>> --- a/nix/nix-daemon/nix-daemon.cc
>> +++ b/nix/nix-daemon/nix-daemon.cc
>> @@ -529,6 +529,11 @@ static void performOp(bool trusted, unsigned int clientVersion,
>>      }
>>  
>>      case wopCollectGarbage: {
>> +        if (settings.isRemoteConnection) {
>> +            throw Error("Garbage collection is disabled for remote hosts.");
>> +            break;
>> +        }
>>          GCOptions options;
>>          options.action = (GCOptions::GCAction) readInt(from);
>>          options.pathsToDelete = readStorePaths<PathSet>(from);
>
> I was wondering if we would like to allow some of the ‘GCAction’ values,
> but maybe it’s better to disallow them altogether like this code does.

Could we please start with a “disable any GC” and start allowing cases
on a case-by-case basis?  The reason I request this, is because it makes
it a lot easier to reason about it from a sysadmin point-of-view.

I'd like to think of it like this: “Garbage collection is effectively
turned off.”.  With the current patch, we can reason about it this way.

>
>> @@ -934,6 +939,7 @@ static void acceptConnection(int fdSocket)
>>                     connection.  Setting these to -1 means: do not change.  */
>>                  settings.clientUid = clientUid;
>>  		settings.clientGid = clientGid;
>> +                settings.isRemoteConnection = (remoteAddr.ss_family != AF_UNIX);
>
> I think you can make ‘isRemoteConnection’ a static global variable in
> nix-daemon.cc instead of adding it to ‘Settings’.  So it would do
> something like:
>
> --8<---------------cut here---------------start------------->8---
> 	/* Fork a child to handle the connection. */
> 	startProcess([&]() {
>                 close(fdSocket);
>
>                 /* Background the daemon. */
>                 if (setsid() == -1)
>                     throw SysError(format("creating a new session"));
>
>                 /* Restore normal handling of SIGCHLD. */
>                 setSigChldAction(false);
>
>                 /* For debugging, stuff the pid into argv[1]. */
>                 if (clientPid != -1 && argvSaved[1]) {
>                     string processName = std::to_string(clientPid);
>                     strncpy(argvSaved[1], processName.c_str(), strlen(argvSaved[1]));
>                 }
>
>                 isRemoteConnection = …;  /*  <– this is the new line */
>
>                 /* Store the client's user and group for this connection. This
>                    has to be done in the forked process since it is per
>                    connection.  Setting these to -1 means: do not change.  */
>                 settings.clientUid = clientUid;
> 		settings.clientGid = clientGid;
> --8<---------------cut here---------------end--------------->8---

Right.  I implemented it using a static global variable in
nix-daemon.cc.  This patch gets shorter and shorter. :)

>
> Last thing: could you add a couple of tests?  tests/guix-daemon.sh
> already has tests for ‘--listen’, so you could take inspiration from
> those.

I included a test, but I don't know how I can properly run this test.
Could you elaborate on how I can test the test(s)?

Kind regards,
Roel Janssen


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From b29d3a90e1487ebda5ac5b6bc146f8c95218eab6 Mon Sep 17 00:00:00 2001
From: Roel Janssen <roel@gnu.org>
Date: Thu, 19 Apr 2018 14:01:49 +0200
Subject: [PATCH] guix-daemon: Disable garbage collection for remote hosts.

* nix/nix-daemon/nix-daemon.cc (performOp): Display appropriate error message;
  (acceptConnection): Set isRemoteConnection when connection is over TCP.
* tests/guix-daemon.sh: Add a test for the new behavior.
---
 nix/nix-daemon/nix-daemon.cc | 10 +++++++++-
 tests/guix-daemon.sh         | 14 ++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/nix/nix-daemon/nix-daemon.cc b/nix/nix-daemon/nix-daemon.cc
index deb7003d7..782e4acfc 100644
--- a/nix/nix-daemon/nix-daemon.cc
+++ b/nix/nix-daemon/nix-daemon.cc
@@ -54,7 +54,9 @@ static FdSink to(STDOUT_FILENO);
 
 bool canSendStderr;
 
-
+/* This variable is used to keep track of whether a connection
+   comes from a host other than the host running guix-daemon. */
+static bool isRemoteConnection;
 
 /* This function is called anytime we want to write something to
    stderr.  If we're in a state where the protocol allows it (i.e.,
@@ -529,6 +531,11 @@ static void performOp(bool trusted, unsigned int clientVersion,
     }
 
     case wopCollectGarbage: {
+        if (isRemoteConnection) {
+            throw Error("Garbage collection is disabled for remote hosts.");
+            break;
+        }
+
         GCOptions options;
         options.action = (GCOptions::GCAction) readInt(from);
         options.pathsToDelete = readStorePaths<PathSet>(from);
@@ -934,6 +941,7 @@ static void acceptConnection(int fdSocket)
                    connection.  Setting these to -1 means: do not change.  */
                 settings.clientUid = clientUid;
 		settings.clientGid = clientGid;
+                isRemoteConnection = (remoteAddr.ss_family != AF_UNIX);
 
                 /* Handle the connection. */
                 from.fd = remote;
diff --git a/tests/guix-daemon.sh b/tests/guix-daemon.sh
index 6f91eb58b..438c79c26 100644
--- a/tests/guix-daemon.sh
+++ b/tests/guix-daemon.sh
@@ -194,6 +194,20 @@ do
     kill "$daemon_pid"
 done
 
+# Make sure garbage collection from a TCP connection does not work.
+
+socket="127.0.0.1:9999"
+guix-daemon --listen="$socket" &
+daemon_pid=$!
+
+output=`GUIX_DAEMON_SOCKET="$socket" guix gc`
+if [[ "$output" != *"GUIX_DAEMON_SOCKET=$socket" ]];
+then
+    exit 1
+fi
+
+kill "$daemon_pid"
+
 # Log compression.
 
 guix-daemon --listen="$socket" --disable-chroot --debug --log-compression=gzip &
-- 
2.17.0