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Cached_fs_rom: fix congestion error

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When the cached_fs_rom saturates the packet stream of its File_system
session it will call the session request handler recursively as pending
transfers are completed. This is bad because the content of the XML node
currently being processed will change.

The session request handler can no longer be called directly, but the
"schedule" method will submit a signal to the request handler, and
requests will be processed after the current operation has completed.
This commit is contained in:
Emery Hemingway 2018-07-12 17:49:56 +02:00 committed by Christian Helmuth
parent ac0562ec18
commit 7e08bba25c
2 changed files with 41 additions and 35 deletions
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19
repos/os/src/server/cached_fs_rom/main.cc
View File

@ -310,18 +310,6 @@ struct Cached_fs_rom::Main final : Genode::Session_request_handler
Io_signal_handler<Main> packet_handler {
env.ep(), *this, &Main::handle_packets };
/**
* Signal handler to disable blocking behavior in 'Expanding_parent_client'
*/
Signal_handler<Main> resource_handler {
env.ep(), *this, &Main::handle_resources };
/**
* Process requests again if parent gives us an upgrade
*/
void handle_resources() {
session_requests.process(); }
/**
* Return true when a cache element is freed
*/
@ -489,7 +477,7 @@ struct Cached_fs_rom::Main final : Genode::Session_request_handler
{
rom.process_packet(pkt);
if (rom.completed())
session_requests.process();
session_requests.schedule();
stray_pkt = false;
});
@ -500,12 +488,13 @@ struct Cached_fs_rom::Main final : Genode::Session_request_handler
Main(Genode::Env &env) : env(env)
{
env.parent().resource_avail_sigh(resource_handler);
/* process the requests when more resources are made available */
env.parent().resource_avail_sigh(session_requests);
fs.sigh_ack_avail(packet_handler);
/* process any requests that have already queued */
session_requests.process();
session_requests.schedule();
}
};

57
repos/os/src/server/cached_fs_rom/session_requests.h
View File

@ -35,7 +35,7 @@ struct Genode::Session_request_handler : Interface
};
class Genode::Session_requests_rom
class Genode::Session_requests_rom : public Signal_handler<Session_requests_rom>
{
private:
@ -44,21 +44,7 @@ class Genode::Session_requests_rom
Attached_rom_dataspace _parent_rom;
Signal_handler<Session_requests_rom> _handler;
public:
Session_requests_rom(Genode::Env &env,
Session_request_handler &requests_handler)
: _parent(env.parent()),
_requests_handler(requests_handler),
_parent_rom(env, "session_requests"),
_handler(env.ep(), *this, &Session_requests_rom::process)
{
_parent_rom.sigh(_handler);
}
void process()
void _process()
{
_parent_rom.update();
Xml_node requests = _parent_rom.xml();
@ -69,10 +55,18 @@ class Genode::Session_requests_rom
request.attribute_value("id", ~0UL) };
typedef Session_state::Name Name;
Name const name = request.attribute_value("service", Name());
typedef Session_state::Args Args;
Args const args = request.sub_node("args").decoded_content<Args>();
Name name { };
Args args { };
try {
name = request.attribute_value("service", Name());
args = request.sub_node("args").decoded_content<Args>();
} catch (...) {
Genode::error("failed to parse request ", request);
return;
}
try { _requests_handler.handle_session_create(name, id, args); }
catch (Service_denied) {
@ -94,7 +88,12 @@ class Genode::Session_requests_rom
request.attribute_value("id", ~0UL) };
typedef Session_state::Args Args;
Args const args = request.sub_node("args").decoded_content<Args>();
Args args { };
try { args = request.sub_node("args").decoded_content<Args>(); }
catch (...) {
Genode::error("failed to parse request ", request);
return;
}
_requests_handler.handle_session_upgrade(id, args);
};
@ -115,6 +114,24 @@ class Genode::Session_requests_rom
/* create new sessions */
requests.for_each_sub_node("create", create_fn);
}
public:
Session_requests_rom(Genode::Env &env,
Session_request_handler &requests_handler)
: Signal_handler<Session_requests_rom>(env.ep(), *this, &Session_requests_rom::_process),
_parent(env.parent()),
_requests_handler(requests_handler),
_parent_rom(env, "session_requests")
{
_parent_rom.sigh(*this);
}
/**
* Post a signal to this requests handler
*/
void schedule() {
Signal_transmitter(*this).submit(); }
};
#endif