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+/*
+ Virtual File System garbage collection code
+
+ Copyright (C) 2003-2023
+ Free Software Foundation, Inc.
+
+ Written by:
+ Miguel de Icaza, 1995
+ Jakub Jelinek, 1995
+ Pavel Machek, 1998
+ Pavel Roskin, 2003
+
+ This file is part of the Midnight Commander.
+
+ The Midnight Commander 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 3 of the License,
+ or (at your option) any later version.
+
+ The Midnight Commander 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, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * \file
+ * \brief Source: Virtual File System: garbage collection code
+ * \author Miguel de Icaza
+ * \author Jakub Jelinek
+ * \author Pavel Machek
+ * \author Pavel Roskin
+ * \date 1995, 1998, 2003
+ */
+
+
+#include <config.h>
+
+#include <stdlib.h>
+
+#include "lib/global.h"
+#include "lib/event.h"
+#include "lib/util.h" /* MC_PTR_FREE */
+
+#include "vfs.h"
+#include "utilvfs.h"
+
+#include "gc.h"
+
+/*
+ * The garbage collection mechanism is based on "stamps".
+ *
+ * A stamp is a record that says "I'm a filesystem which is no longer in
+ * use. Free me when you get a chance."
+ *
+ * This file contains a set of functions used for managing this stamp. You
+ * should use them when you write your own filesystem. Here are some rules
+ * of thumb:
+ *
+ * (1) When the last open file in your filesystem gets closed, conditionally
+ * create a stamp. You do this with vfs_stamp_create(). (The meaning
+ * of "conditionally" is explained below.)
+ *
+ * (2) When a file in your filesystem is opened, delete the stamp. You do
+ * this with vfs_rmstamp().
+ *
+ * (3) When a path inside your filesystem is invoked, call vfs_stamp() to
+ * postpone the free'ing of your filesystem a bit. (This simply updates
+ * a timestamp variable inside the stamp.)
+ *
+ * Additionally, when a user navigates to a new directory in a panel (or a
+ * programmer uses mc_chdir()), a stamp is conditionally created for the
+ * previous directory's filesystem. This ensures that that filesystem is
+ * free'ed. (see: _do_panel_cd() -> vfs_release_path(); mc_chdir()).
+ *
+ * We've spoken here of "conditionally creating" a stamp. What we mean is
+ * that vfs_stamp_create() is to be used: this function creates a stamp
+ * only if no directories are open (aka "active") in your filesystem. (If
+ * there _are_ directories open, it means that the filesystem is in use, in
+ * which case we don't want to free it.)
+ */
+
+/*** global variables ****************************************************************************/
+
+int vfs_timeout = 60; /* VFS timeout in seconds */
+
+/*** file scope macro definitions ****************************************************************/
+
+#define VFS_STAMPING(a) ((struct vfs_stamping *)(a))
+
+/*** file scope type declarations ****************************************************************/
+
+struct vfs_stamping
+{
+ struct vfs_class *v;
+ vfsid id;
+ gint64 time;
+};
+
+/*** forward declarations (file scope functions) *************************************************/
+
+/*** file scope variables ************************************************************************/
+
+static GSList *stamps = NULL;
+
+/* --------------------------------------------------------------------------------------------- */
+/*** file scope functions ************************************************************************/
+/* --------------------------------------------------------------------------------------------- */
+
+static gint
+vfs_stamp_compare (gconstpointer a, gconstpointer b)
+{
+ const struct vfs_stamping *vsa = (const struct vfs_stamping *) a;
+ const struct vfs_stamping *vsb = (const struct vfs_stamping *) b;
+
+ return (vsa == NULL || vsb == NULL || (vsa->v == vsb->v && vsa->id == vsb->id)) ? 0 : 1;
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+static void
+vfs_addstamp (struct vfs_class *v, vfsid id)
+{
+ if ((v->flags & VFSF_LOCAL) == 0 && id != NULL && !vfs_stamp (v, id))
+ {
+ struct vfs_stamping *stamp;
+
+ stamp = g_new (struct vfs_stamping, 1);
+ stamp->v = v;
+ stamp->id = id;
+ stamp->time = g_get_monotonic_time ();
+
+ stamps = g_slist_append (stamps, stamp);
+ }
+}
+
+/* --------------------------------------------------------------------------------------------- */
+/*** public functions ****************************************************************************/
+/* --------------------------------------------------------------------------------------------- */
+
+gboolean
+vfs_stamp (struct vfs_class *v, vfsid id)
+{
+ struct vfs_stamping what = {
+ .v = v,
+ .id = id
+ };
+ GSList *stamp;
+ gboolean ret = FALSE;
+
+ stamp = g_slist_find_custom (stamps, &what, vfs_stamp_compare);
+ if (stamp != NULL && stamp->data != NULL)
+ {
+ VFS_STAMPING (stamp->data)->time = g_get_monotonic_time ();
+ ret = TRUE;
+ }
+
+ return ret;
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+void
+vfs_rmstamp (struct vfs_class *v, vfsid id)
+{
+ struct vfs_stamping what = {
+ .v = v,
+ .id = id
+ };
+ GSList *stamp;
+
+ stamp = g_slist_find_custom (stamps, &what, vfs_stamp_compare);
+ if (stamp != NULL)
+ {
+ g_free (stamp->data);
+ stamps = g_slist_delete_link (stamps, stamp);
+ }
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+void
+vfs_stamp_path (const vfs_path_t * vpath)
+{
+ vfsid id;
+ struct vfs_class *me;
+
+ me = VFS_CLASS (vfs_path_get_last_path_vfs (vpath));
+ id = vfs_getid (vpath);
+ vfs_addstamp (me, id);
+}
+
+/* --------------------------------------------------------------------------------------------- */
+/**
+ * Create a new timestamp item by VFS class and VFS id.
+ */
+
+void
+vfs_stamp_create (struct vfs_class *vclass, vfsid id)
+{
+ vfsid nvfsid;
+
+ ev_vfs_stamp_create_t event_data = { vclass, id, FALSE };
+ const vfs_path_t *vpath;
+ struct vfs_class *me;
+
+ /* There are three directories we have to take care of: current_dir,
+ current_panel->cwd and other_panel->cwd. Although most of the time either
+ current_dir and current_panel->cwd or current_dir and other_panel->cwd are the
+ same, it's possible that all three are different -- Norbert */
+
+ if (!mc_event_present (MCEVENT_GROUP_CORE, "vfs_timestamp"))
+ return;
+
+ vpath = vfs_get_raw_current_dir ();
+ me = VFS_CLASS (vfs_path_get_last_path_vfs (vpath));
+
+ nvfsid = vfs_getid (vpath);
+ vfs_rmstamp (me, nvfsid);
+
+ if (!(id == NULL || (me == vclass && nvfsid == id)))
+ {
+ mc_event_raise (MCEVENT_GROUP_CORE, "vfs_timestamp", (gpointer) & event_data);
+
+ if (!event_data.ret && vclass != NULL && vclass->nothingisopen != NULL
+ && vclass->nothingisopen (id))
+ vfs_addstamp (vclass, id);
+ }
+}
+
+/* --------------------------------------------------------------------------------------------- */
+/** This is called from timeout handler with now = FALSE,
+ or can be called with now = TRUE to force freeing all filesystems */
+
+void
+vfs_expire (gboolean now)
+{
+ static gboolean locked = FALSE;
+ gint64 curr_time, exp_time;
+ GSList *stamp;
+
+ /* Avoid recursive invocation, e.g. when one of the free functions
+ calls message */
+ if (locked)
+ return;
+ locked = TRUE;
+
+ curr_time = g_get_monotonic_time ();
+ exp_time = curr_time - vfs_timeout * G_USEC_PER_SEC;
+
+ if (now)
+ {
+ /* reverse list to free nested VFSes at first */
+ stamps = g_slist_reverse (stamps);
+ }
+
+ /* NULLize stamps that point to expired VFS */
+ for (stamp = stamps; stamp != NULL; stamp = g_slist_next (stamp))
+ {
+ struct vfs_stamping *stamping = VFS_STAMPING (stamp->data);
+
+ if (now)
+ {
+ /* free VFS forced */
+ if (stamping->v->free != NULL)
+ stamping->v->free (stamping->id);
+ MC_PTR_FREE (stamp->data);
+ }
+ else if (stamping->time <= exp_time)
+ {
+ /* update timestamp of VFS that is in use, or free unused VFS */
+ if (stamping->v->nothingisopen != NULL && !stamping->v->nothingisopen (stamping->id))
+ stamping->time = curr_time;
+ else
+ {
+ if (stamping->v->free != NULL)
+ stamping->v->free (stamping->id);
+ MC_PTR_FREE (stamp->data);
+ }
+ }
+ }
+
+ /* then remove NULLized stamps */
+ stamps = g_slist_remove_all (stamps, NULL);
+
+ locked = FALSE;
+}
+
+/* --------------------------------------------------------------------------------------------- */
+/*
+ * Return the number of seconds remaining to the vfs timeout.
+ * FIXME: The code should be improved to actually return the number of
+ * seconds until the next item times out.
+ */
+
+int
+vfs_timeouts (void)
+{
+ return stamps != NULL ? 10 : 0;
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+void
+vfs_timeout_handler (void)
+{
+ vfs_expire (FALSE);
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+void
+vfs_release_path (const vfs_path_t * vpath)
+{
+ vfsid id;
+ struct vfs_class *me;
+
+ me = VFS_CLASS (vfs_path_get_last_path_vfs (vpath));
+ id = vfs_getid (vpath);
+ vfs_stamp_create (me, id);
+}
+
+/* --------------------------------------------------------------------------------------------- */
+/* Free all data */
+
+void
+vfs_gc_done (void)
+{
+ vfs_expire (TRUE);
+}
+
+/* --------------------------------------------------------------------------------------------- */
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