kernel: reference count mount objects, free them on process kills

4 files changed, 34 insertions, 2 deletions

diff --git a/src/kernel/proc.c b/src/kernel/proc.c
index ba19943..90570b8 100644
--- a/src/kernel/proc.c
+++ b/src/kernel/proc.c
@@ -72,6 +72,9 @@ struct process *process_fork(struct process *parent, int flags) {
 		// no overflow check - if you manage to get 2^32 references to a handle you have bigger problems
 	}
 
+	assert(child->mount);
+	child->mount->refs++;
+
 	child->id = next_pid++;
 
 	return child;
@@ -104,6 +107,10 @@ void process_free(struct process *p) {
 	while (p->child)
 		process_free(p->child);
 
+	// also could be done on kill
+	vfs_mount_remref(p->mount);
+	p->mount = NULL;
+
 	if (!p->parent) return;
 	process_forget(p);
 	pagedir_free(p->pages); // TODO could be done on kill
diff --git a/src/kernel/syscalls.c b/src/kernel/syscalls.c
index 57286f1..7748bc5 100644
--- a/src/kernel/syscalls.c
+++ b/src/kernel/syscalls.c
@@ -109,12 +109,17 @@ int _syscall_mount(handle_t hid, const char __user *path, int len) {
 	} // otherwise backend == NULL
 
 	// append to mount list
+	// TODO move to kernel/vfs/mount.c
 	mount = kmalloc(sizeof *mount);
 	mount->prev = process_current->mount;
-	mount->prefix = path_buf;
+	mount->prefix = path_buf; // owned
 	mount->prefix_len = len;
 	mount->backend = backend;
+	mount->refs = 1;
 	process_current->mount = mount;
+
+	kmalloc_sanity(mount);
+	kmalloc_sanity(mount->prefix);
 	return 0;
 
 fail:
diff --git a/src/kernel/vfs/mount.c b/src/kernel/vfs/mount.c
index 423bf10..3fe192d 100644
--- a/src/kernel/vfs/mount.c
+++ b/src/kernel/vfs/mount.c
@@ -1,4 +1,5 @@
 #include <kernel/mem/alloc.h>
+#include <kernel/panic.h>
 #include <kernel/vfs/mount.h>
 #include <shared/mem.h>
 
@@ -9,9 +10,10 @@ struct vfs_mount *vfs_mount_seed(void) {
 	backend->potential_handlers = 1;
 	*mount = (struct vfs_mount){
 		.prev = NULL,
-		.prefix = "",
+		.prefix = NULL,
 		.prefix_len = 0,
 		.backend = backend,
+		.refs = 1, // never to be freed
 	};
 	return mount;
 }
@@ -36,3 +38,15 @@ struct vfs_mount *vfs_mount_resolve(
 	}
 	return top;
 }
+
+void vfs_mount_remref(struct vfs_mount *mnt) {
+	assert(mnt);
+	assert(mnt->refs > 0);
+	if (--(mnt->refs) > 0) return;
+
+	struct vfs_mount *prev = mnt->prev;
+	kfree(mnt->prefix);
+	kfree(mnt);
+
+	if (prev) vfs_mount_remref(prev);
+}
diff --git a/src/kernel/vfs/mount.h b/src/kernel/vfs/mount.h
index 5fb6d16..96a2d7b 100644
--- a/src/kernel/vfs/mount.h
+++ b/src/kernel/vfs/mount.h
@@ -7,9 +7,15 @@ struct vfs_mount {
 	char *prefix;
 	size_t prefix_len;
 	struct vfs_backend *backend;
+	size_t refs; /* counts all references, atm from:
+	              *  - struct vfs_mount
+	              *  - struct proc
+	              */
 };
 
 // prepares init's filesystem view
 struct vfs_mount *vfs_mount_seed(void);
 struct vfs_mount *vfs_mount_resolve(
 		struct vfs_mount *top, const char *path, size_t path_len);
+/** Decrements the reference count, potentially freeing the mount. */
+void vfs_mount_remref(struct vfs_mount *mnt);