libpager: Add pager_get_ro_port ()

A pager will now maintain a port to a read-only memory object proxy
for itself, and let the users access it with pager_get_ro_port ().

6 files changed, 73 insertions, 1 deletions

diff --git a/libpager/Makefile b/libpager/Makefile
index 72b4bfdc..06fcb96b 100644
--- a/libpager/Makefile
+++ b/libpager/Makefile
@@ -24,7 +24,7 @@ SRCS = data-request.c data-return.c data-unlock.c pager-port.c \
 	pager-create.c pager-flush.c pager-shutdown.c pager-sync.c \
 	stubs.c demuxer.c chg-compl.c pager-attr.c clean.c \
 	dropweak.c get-upi.c pager-memcpy.c pager-return.c \
-	offer-page.c
+	offer-page.c pager-ro-port.c
 installhdrs = pager.h
 
 HURDLIBS= ports
diff --git a/libpager/object-terminate.c b/libpager/object-terminate.c
index 3e7df167..8e8205b5 100644
--- a/libpager/object-terminate.c
+++ b/libpager/object-terminate.c
@@ -115,6 +115,11 @@ _pager_free_structure (struct pager *p)
       mach_port_deallocate (mach_task_self (), p->memobjname);
       p->memobjname = MACH_PORT_NULL;
     }
+  if (p->ro_proxy != MACH_PORT_NULL)
+    {
+      mach_port_deallocate (mach_task_self (), p->ro_proxy);
+      p->ro_proxy = MACH_PORT_NULL;
+    }
 
   /* Free the pagemap */
   if (p->pagemapsize)
diff --git a/libpager/pager-create.c b/libpager/pager-create.c
index 7f2f7d6e..9c3fba99 100644
--- a/libpager/pager-create.c
+++ b/libpager/pager-create.c
@@ -42,6 +42,7 @@ _pager_create (size_t size,
   p->notify_on_evict = notify_on_evict;
   p->memobjcntl = MACH_PORT_NULL;
   p->memobjname = MACH_PORT_NULL;
+  p->ro_proxy = MACH_PORT_NULL;
   p->noterm = 0;
   p->termwaiting = 0;
   p->pagemap = 0;
diff --git a/libpager/pager-ro-port.c b/libpager/pager-ro-port.c
new file mode 100644
index 00000000..713b0423
--- /dev/null
+++ b/libpager/pager-ro-port.c
@@ -0,0 +1,61 @@
+/* Copyright (C) 2021 Free Software Foundation, Inc.
+
+   Written by Sergey Bugaev <bugaevc@gmail.com>.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
+
+#include "priv.h"
+#include <mach/mach4.h>
+
+mach_port_t
+pager_get_ro_port (struct pager *p)
+{
+  error_t err = 0;;
+  mach_port_t port = MACH_PORT_NULL;
+  mach_port_t rw_port;
+  vm_offset_t offset = 0;
+  vm_offset_t start = 0;
+  vm_size_t len = ~0;
+
+  pthread_mutex_lock (&p->interlock);
+
+  if (!MACH_PORT_VALID (p->ro_proxy))
+    {
+      rw_port = ports_get_send_right (p);
+      if (!MACH_PORT_VALID (rw_port))
+        {
+          err = errno;
+          goto out;
+        }
+
+      err = memory_object_create_proxy (mach_task_self (),
+                                        VM_PROT_READ | VM_PROT_EXECUTE,
+                                        &rw_port, 1,
+                                        &offset, 1, &start, 1, &len, 1,
+                                        &p->ro_proxy);
+
+      mach_port_deallocate (mach_task_self (), rw_port);
+
+      if (err)
+        goto out;
+    }
+
+  port = p->ro_proxy;
+
+ out:
+  pthread_mutex_unlock (&p->interlock);
+  errno = err;
+  return port;
+}
diff --git a/libpager/pager.h b/libpager/pager.h
index dd8026a7..16b47def 100644
--- a/libpager/pager.h
+++ b/libpager/pager.h
@@ -155,6 +155,9 @@ pager_change_attributes (struct pager *pager,
 mach_port_t
 pager_get_port (struct pager *pager);
 
+mach_port_t
+pager_get_ro_port (struct pager *pager);
+
 /* Force termination of a pager.  After this returns, no
    more paging requests on the pager will be honored, and the
    pager will be deallocated.  (The actual deallocation might
diff --git a/libpager/priv.h b/libpager/priv.h
index 89af52ba..0c38a7c0 100644
--- a/libpager/priv.h
+++ b/libpager/priv.h
@@ -55,6 +55,8 @@ struct pager
   memory_object_control_t memobjcntl;
   memory_object_name_t memobjname;
 
+  memory_object_t ro_proxy;
+
   int noterm;			/* number of threads blocking termination */
 
   int termwaiting:1;