journal: replace contexts hashmap with a plain array

[elogind.git] / src / journal / mmap-cache.c

diff --git a/src/journal/mmap-cache.c b/src/journal/mmap-cache.c
index 7dbbb5ef381b4c6b617441c4a6dae2c74aae9ca3..4c940aaa24afb9a3a7f6371f8c5ce5fb146eeea2 100644 (file)
--- a/src/journal/mmap-cache.c
+++ b/src/journal/mmap-cache.c
@@ -38,7 +38,7 @@ typedef struct FileDescriptor FileDescriptor;
 struct Window {
         MMapCache *cache;
 
-        unsigned keep_always;
+        bool keep_always;
         bool in_unused;
 
         int prot;
@@ -76,14 +76,20 @@ struct MMapCache {
 
 
         Hashmap *fds;
-        Hashmap *contexts;
+        Context *contexts[MMAP_CACHE_MAX_CONTEXTS];
 
         LIST_HEAD(Window, unused);
         Window *last_unused;
 };
 
 #define WINDOWS_MIN 64
-#define WINDOW_SIZE (8ULL*1024ULL*1024ULL)
+
+#ifdef ENABLE_DEBUG_MMAP_CACHE
+/* Tiny windows increase mmap activity and the chance of exposing unsafe use. */
+# define WINDOW_SIZE (page_size())
+#else
+# define WINDOW_SIZE (8ULL*1024ULL*1024ULL)
+#endif
 
 MMapCache* mmap_cache_new(void) {
         MMapCache *m;
@@ -185,13 +191,19 @@ static void context_detach_window(Context *c) {
         c->window = NULL;
         LIST_REMOVE(by_window, w->contexts, c);
 
-        if (!w->contexts && w->keep_always == 0) {
+        if (!w->contexts && !w->keep_always) {
                 /* Not used anymore? */
+#ifdef ENABLE_DEBUG_MMAP_CACHE
+                /* Unmap unused windows immediately to expose use-after-unmap
+                 * by SIGSEGV. */
+                window_free(w);
+#else
                 LIST_PREPEND(unused, c->cache->unused, w);
                 if (!c->cache->last_unused)
                         c->cache->last_unused = w;
 
                 w->in_unused = true;
+#endif
         }
 }
 
@@ -219,18 +231,13 @@ static void context_attach_window(Context *c, Window *w) {
 
 static Context *context_add(MMapCache *m, unsigned id) {
         Context *c;
-        int r;
 
         assert(m);
 
-        c = hashmap_get(m->contexts, UINT_TO_PTR(id + 1));
+        c = m->contexts[id];
         if (c)
                 return c;
 
-        r = hashmap_ensure_allocated(&m->contexts, trivial_hash_func, trivial_compare_func);
-        if (r < 0)
-                return NULL;
-
         c = new0(Context, 1);
         if (!c)
                 return NULL;
@@ -238,11 +245,8 @@ static Context *context_add(MMapCache *m, unsigned id) {
         c->cache = m;
         c->id = id;
 
-        r = hashmap_put(m->contexts, UINT_TO_PTR(id + 1), c);
-        if (r < 0) {
-                free(c);
-                return NULL;
-        }
+        assert(!m->contexts[id]);
+        m->contexts[id] = c;
 
         return c;
 }
@@ -252,8 +256,10 @@ static void context_free(Context *c) {
 
         context_detach_window(c);
 
-        if (c->cache)
-                assert_se(hashmap_remove(c->cache->contexts, UINT_TO_PTR(c->id + 1)));
+        if (c->cache) {
+                assert(c->cache->contexts[c->id] == c);
+                c->cache->contexts[c->id] = NULL;
+        }
 
         free(c);
 }
@@ -281,7 +287,7 @@ static FileDescriptor* fd_add(MMapCache *m, int fd) {
         if (f)
                 return f;
 
-        r = hashmap_ensure_allocated(&m->fds, trivial_hash_func, trivial_compare_func);
+        r = hashmap_ensure_allocated(&m->fds, NULL);
         if (r < 0)
                 return NULL;
 
@@ -302,15 +308,14 @@ static FileDescriptor* fd_add(MMapCache *m, int fd) {
 }
 
 static void mmap_cache_free(MMapCache *m) {
-        Context *c;
         FileDescriptor *f;
+        int i;
 
         assert(m);
 
-        while ((c = hashmap_first(m->contexts)))
-                context_free(c);
-
-        hashmap_free(m->contexts);
+        for (i = 0; i < MMAP_CACHE_MAX_CONTEXTS; i++)
+                if (m->contexts[i])
+                        context_free(m->contexts[i]);
 
         while ((f = hashmap_first(m->fds)))
                 fd_free(f);
@@ -360,8 +365,9 @@ static int try_context(
         assert(m->n_ref > 0);
         assert(fd >= 0);
         assert(size > 0);
+        assert(ret);
 
-        c = hashmap_get(m->contexts, UINT_TO_PTR(context+1));
+        c = m->contexts[context];
         if (!c)
                 return 0;
 
@@ -377,10 +383,9 @@ static int try_context(
                 return 0;
         }
 
-        c->window->keep_always += keep_always;
+        c->window->keep_always |= keep_always;
 
-        if (ret)
-                *ret = (uint8_t*) c->window->ptr + (offset - c->window->offset);
+        *ret = (uint8_t*) c->window->ptr + (offset - c->window->offset);
         return 1;
 }
 
@@ -423,8 +428,7 @@ static int find_mmap(
         context_attach_window(c, w);
         w->keep_always += keep_always;
 
-        if (ret)
-                *ret = (uint8_t*) w->ptr + (offset - w->offset);
+        *ret = (uint8_t*) w->ptr + (offset - w->offset);
         return 1;
 }
 
@@ -450,6 +454,7 @@ static int add_mmap(
         assert(m->n_ref > 0);
         assert(fd >= 0);
         assert(size > 0);
+        assert(ret);
 
         woffset = offset & ~((uint64_t) page_size() - 1ULL);
         wsize = size + (offset - woffset);
@@ -496,15 +501,15 @@ static int add_mmap(
 
         c = context_add(m, context);
         if (!c)
-                return -ENOMEM;
+                goto outofmem;
 
         f = fd_add(m, fd);
         if (!f)
-                return -ENOMEM;
+                goto outofmem;
 
         w = window_add(m);
         if (!w)
-                return -ENOMEM;
+                goto outofmem;
 
         w->keep_always = keep_always;
         w->ptr = d;
@@ -519,9 +524,12 @@ static int add_mmap(
         c->window = w;
         LIST_PREPEND(by_window, w->contexts, c);
 
-        if (ret)
-                *ret = (uint8_t*) w->ptr + (offset - w->offset);
+        *ret = (uint8_t*) w->ptr + (offset - w->offset);
         return 1;
+
+outofmem:
+        munmap(d, wsize);
+        return -ENOMEM;
 }
 
 int mmap_cache_get(
@@ -541,6 +549,8 @@ int mmap_cache_get(
         assert(m->n_ref > 0);
         assert(fd >= 0);
         assert(size > 0);
+        assert(ret);
+        assert(context < MMAP_CACHE_MAX_CONTEXTS);
 
         /* Check whether the current context is the right one already */
         r = try_context(m, fd, prot, context, keep_always, offset, size, ret);
@@ -562,42 +572,6 @@ int mmap_cache_get(
         return add_mmap(m, fd, prot, context, keep_always, offset, size, st, ret);
 }
 
-int mmap_cache_release(
-                MMapCache *m,
-                int fd,
-                int prot,
-                unsigned context,
-                uint64_t offset,
-                size_t size) {
-
-        FileDescriptor *f;
-        Window *w;
-
-        assert(m);
-        assert(m->n_ref > 0);
-        assert(fd >= 0);
-        assert(size > 0);
-
-        f = hashmap_get(m->fds, INT_TO_PTR(fd + 1));
-        if (!f)
-                return -EBADF;
-
-        assert(f->fd == fd);
-
-        LIST_FOREACH(by_fd, w, f->windows)
-                if (window_matches(w, fd, prot, offset, size))
-                        break;
-
-        if (!w)
-                return -ENOENT;
-
-        if (w->keep_always == 0)
-                return -ENOLCK;
-
-        w->keep_always -= 1;
-        return 0;
-}
-
 void mmap_cache_close_fd(MMapCache *m, int fd) {
         FileDescriptor *f;
 
@@ -611,18 +585,6 @@ void mmap_cache_close_fd(MMapCache *m, int fd) {
         fd_free(f);
 }
 
-void mmap_cache_close_context(MMapCache *m, unsigned context) {
-        Context *c;
-
-        assert(m);
-
-        c = hashmap_get(m->contexts, UINT_TO_PTR(context + 1));
-        if (!c)
-                return;
-
-        context_free(c);
-}
-
 unsigned mmap_cache_get_hit(MMapCache *m) {
         assert(m);