Changeset 5a324099 in mainline

Timestamp:

2008-05-04T16:17:01Z (16 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

0c1ad7ac

Parents:

f520905

Message:

Code for de/allocation of VFS indices for FAT.

Location:

uspace/srv/fs/fat

Files:

• fat.h (modified) (1 diff)
• fat_idx.c (modified) (2 diffs)
• fat_ops.c (modified) (1 diff)

uspace/srv/fs/fat/fat.h

@@ -215 +215 @@
 extern void fat_lookup(ipc_callid_t, ipc_call_t *);
 
-extern fat_idx_t *fat_idx_map(fat_cluster_t, unsigned);
+extern fat_idx_t *fat_idx_map(dev_handle_t, fat_cluster_t, unsigned);
 
 #endif

uspace/srv/fs/fat/fat_idx.c

@@ -37 +37 @@
 
 #include "fat.h"
+#include "../../vfs/vfs.h"
 #include <errno.h>
 #include <string.h>
@@ -44 +45 @@
 #include <futex.h>
 
-fat_idx_t *fat_idx_map(fat_cluster_t pfc, unsigned pdi)
+/** Each instance of this type describes one interval of freed VFS indices. */
+typedef struct {
+        link_t          link;
+        fs_index_t      first;
+        fs_index_t      last;
+} freed_t;
+
+/**
+ * Each instance of this type describes state of all VFS indices that
+ * are currently unused.
+ */
+typedef struct {
+        link_t          link;
+        dev_handle_t    dev_handle;
+
+        /** Next unassigned index. */
+        fs_index_t      next;
+        /** Number of remaining unassigned indices. */
+        uint64_t        remaining;
+
+        /** Sorted list of intervals of freed indices. */
+        link_t          freed_head;
+} unused_t;
+
+static LIST_INITIALIZE(unused_head);
+
+/** Allocate a VFS index which is not currently in use. */
+static bool fat_idx_alloc(dev_handle_t dev_handle, fs_index_t *index)
+{
+        link_t *l;
+        unused_t *u;
+        
+        assert(index);
+        for (l = unused_head.next; l != &unused_head; l = l->next) {
+                u = list_get_instance(l, unused_t, link);
+                if (u->dev_handle == dev_handle) 
+                        goto hit;
+        }
+
+        /* dev_handle not found */
+        return false;   
+
+hit:
+        if (list_empty(&u->freed_head)) {
+                if (u->remaining) { 
+                        /*
+                         * There are no freed indices, allocate one directly
+                         * from the counter.
+                         */
+                        *index = u->next++;
+                        --u->remaining;
+                        return true;
+                }
+        } else {
+                /* There are some freed indices which we can reuse. */
+                freed_t *f = list_get_instance(u->freed_head.next, freed_t,
+                    link);
+                *index = f->first;
+                if (f->first++ == f->last) {
+                        /* Destroy the interval. */
+                        list_remove(&f->link);
+                        free(f);
+                }
+                return true;
+        }
+        /*
+         * We ran out of indices, which is extremely unlikely with FAT16, but
+         * theoretically still possible (e.g. too many open unlinked nodes or
+         * too many zero-sized nodes).
+         */
+        return false;
+}
+
+/** If possible, merge two intervals of freed indices. */
+static void try_merge_intervals(link_t *l, link_t *r, link_t *cur)
+{
+        freed_t *fl = list_get_instance(l, freed_t, link);
+        freed_t *fr = list_get_instance(r, freed_t, link);
+
+        if (fl->last + 1 == fr->first) {
+                if (cur == l) {
+                        fl->last = fr->last;
+                        list_remove(r);
+                        free(r);
+                } else {
+                        fr->first = fl->first;
+                        list_remove(l);
+                        free(l);
+                }
+        }
+}
+
+/** Free a VFS index, which is no longer in use. */
+static void fat_idx_free(dev_handle_t dev_handle, fs_index_t index)
+{
+        link_t *l;
+        unused_t *u;
+
+        for (l = unused_head.next; l != &unused_head; l = l->next) {
+                u = list_get_instance(l, unused_t, link);
+                if (u->dev_handle == dev_handle)
+                        goto hit;
+        }
+
+        /* should not happen */
+        assert(0);
+
+hit:
+        if (u->next == index + 1) {
+                /* The index can be returned directly to the counter. */
+                u->next--;
+                u->remaining++;
+                return;
+        } else {
+                /*
+                 * The index must be returned either to an existing freed
+                 * interval or a new interval must be created.
+                 */
+                link_t *lnk;
+                freed_t *n;
+                for (lnk = u->freed_head.next; lnk != &u->freed_head;
+                    lnk = lnk->next) {
+                        freed_t *f = list_get_instance(lnk, freed_t, link);
+                        if (f->first == index + 1) {
+                                f->first--;
+                                if (lnk->prev != &u->freed_head)
+                                        try_merge_intervals(lnk->prev, lnk,
+                                            lnk);
+                                return;
+                        }
+                        if (f->last == index - 1) {
+                                f->last++;
+                                if (lnk->next != &u->freed_head)
+                                        try_merge_intervals(lnk, lnk->next,
+                                            lnk);
+                                return;
+                        }
+                        if (index > f->first) {
+                                n = malloc(sizeof(freed_t));
+                                /* TODO: sleep until allocation succeeds */
+                                assert(n);
+                                link_initialize(&n->link);
+                                n->first = index;
+                                n->last = index;
+                                list_insert_before(&n->link, lnk);
+                                return;
+                        }
+
+                }
+                /* The index will form the last interval. */
+                n = malloc(sizeof(freed_t));
+                /* TODO: sleep until allocation succeeds */
+                assert(n);
+                link_initialize(&n->link);
+                n->first = index;
+                n->last = index;
+                list_append(&n->link, &u->freed_head);
+        }
+}
+
+fat_idx_t *fat_idx_map(dev_handle_t dev_handle, fat_cluster_t pfc, unsigned pdi)
 {
         return NULL;    /* TODO */

uspace/srv/fs/fat/fat_ops.c

@@ -309 +309 @@
                         if (strcmp(name, component) == 0) {
                                 /* hit */
-                                fat_idx_t *idx = fat_idx_map(parentp->firstc,
+                                fat_idx_t *idx = fat_idx_map(
+                                    parentp->idx->dev_handle, parentp->firstc,
                                     i * dps + j);
                                 void *node = fat_node_get(idx->dev_handle,