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 7813f037544546fe8bf8e33c85c6768acce001a0..4c940aaa24afb9a3a7f6371f8c5ce5fb146eeea2 100644 (file)
--- a/src/journal/mmap-cache.c
+++ b/src/journal/mmap-cache.c
@@ -41,9 +41,9 @@ struct Window {
         bool keep_always;
         bool in_unused;
 
+        int prot;
         void *ptr;
         uint64_t offset;
-        int prot;
         size_t size;
 
         FileDescriptor *fd;
@@ -70,18 +70,26 @@ struct FileDescriptor {
 
 struct MMapCache {
         int n_ref;
+        unsigned n_windows;
 
-        Hashmap *fds;
-        Hashmap *contexts;
+        unsigned n_hit, n_missed;
 
-        unsigned n_windows;
+
+        Hashmap *fds;
+        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;
@@ -111,13 +119,13 @@ static void window_unlink(Window *w) {
                 munmap(w->ptr, w->size);
 
         if (w->fd)
-                LIST_REMOVE(Window, by_fd, w->fd->windows, w);
+                LIST_REMOVE(by_fd, w->fd->windows, w);
 
         if (w->in_unused) {
                 if (w->cache->last_unused == w)
                         w->cache->last_unused = w->unused_prev;
 
-                LIST_REMOVE(Window, unused, w->cache->unused, w);
+                LIST_REMOVE(unused, w->cache->unused, w);
         }
 
         LIST_FOREACH(by_window, c, w->contexts) {
@@ -134,7 +142,7 @@ static void window_free(Window *w) {
         free(w);
 }
 
-static bool window_matches(Window *w, int fd, int prot, uint64_t offset, size_t size) {
+_pure_ static bool window_matches(Window *w, int fd, int prot, uint64_t offset, size_t size) {
         assert(w);
         assert(fd >= 0);
         assert(size > 0);
@@ -181,15 +189,21 @@ static void context_detach_window(Context *c) {
 
         w = c->window;
         c->window = NULL;
-        LIST_REMOVE(Context, by_window, w->contexts, c);
+        LIST_REMOVE(by_window, w->contexts, c);
 
         if (!w->contexts && !w->keep_always) {
                 /* Not used anymore? */
-                LIST_PREPEND(Window, unused, c->cache->unused, w);
+#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
         }
 }
 
@@ -204,31 +218,26 @@ static void context_attach_window(Context *c, Window *w) {
 
         if (w->in_unused) {
                 /* Used again? */
-                LIST_REMOVE(Window, unused, c->cache->unused, w);
-                if (!c->cache->last_unused)
-                        c->cache->last_unused = w;
+                LIST_REMOVE(unused, c->cache->unused, w);
+                if (c->cache->last_unused == w)
+                        c->cache->last_unused = w->unused_prev;
 
                 w->in_unused = false;
         }
 
         c->window = w;
-        LIST_PREPEND(Context, by_window, w->contexts, c);
+        LIST_PREPEND(by_window, w->contexts, c);
 }
 
 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;
@@ -236,11 +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;
 }
@@ -250,8 +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);
 }
@@ -279,7 +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;
 
@@ -300,17 +308,20 @@ 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);
+        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);
 
+        hashmap_free(m->fds);
+
         while (m->unused)
                 window_free(m->unused);
 
@@ -356,7 +367,7 @@ static int try_context(
         assert(size > 0);
         assert(ret);
 
-        c = hashmap_get(m->contexts, UINT_TO_PTR(context+1));
+        c = m->contexts[context];
         if (!c)
                 return 0;
 
@@ -372,7 +383,7 @@ static int try_context(
                 return 0;
         }
 
-        c->window->keep_always = c->window->keep_always || keep_always;
+        c->window->keep_always |= keep_always;
 
         *ret = (uint8_t*) c->window->ptr + (offset - c->window->offset);
         return 1;
@@ -396,7 +407,6 @@ static int find_mmap(
         assert(m->n_ref > 0);
         assert(fd >= 0);
         assert(size > 0);
-        assert(ret);
 
         f = hashmap_get(m->fds, INT_TO_PTR(fd + 1));
         if (!f)
@@ -416,7 +426,7 @@ static int find_mmap(
                 return -ENOMEM;
 
         context_attach_window(c, w);
-        w->keep_always = w->keep_always || keep_always;
+        w->keep_always += keep_always;
 
         *ret = (uint8_t*) w->ptr + (offset - w->offset);
         return 1;
@@ -491,15 +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;
@@ -508,14 +518,18 @@ static int add_mmap(
         w->size = wsize;
         w->fd = f;
 
-        LIST_PREPEND(Window, by_fd, f->windows, w);
+        LIST_PREPEND(by_fd, f->windows, w);
 
         context_detach_window(c);
         c->window = w;
-        LIST_PREPEND(Context, by_window, w->contexts, c);
+        LIST_PREPEND(by_window, w->contexts, c);
 
         *ret = (uint8_t*) w->ptr + (offset - w->offset);
         return 1;
+
+outofmem:
+        munmap(d, wsize);
+        return -ENOMEM;
 }
 
 int mmap_cache_get(
@@ -536,16 +550,23 @@ int mmap_cache_get(
         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);
-        if (r != 0)
+        if (r != 0) {
+                m->n_hit ++;
                 return r;
+        }
 
         /* Search for a matching mmap */
         r = find_mmap(m, fd, prot, context, keep_always, offset, size, ret);
-        if (r != 0)
+        if (r != 0) {
+                m->n_hit ++;
                 return r;
+        }
+
+        m->n_missed++;
 
         /* Create a new mmap */
         return add_mmap(m, fd, prot, context, keep_always, offset, size, st, ret);
@@ -564,14 +585,14 @@ void mmap_cache_close_fd(MMapCache *m, int fd) {
         fd_free(f);
 }
 
-void mmap_cache_close_context(MMapCache *m, unsigned context) {
-        Context *c;
-
+unsigned mmap_cache_get_hit(MMapCache *m) {
         assert(m);
 
-        c = hashmap_get(m->contexts, UINT_TO_PTR(context + 1));
-        if (!c)
-                return;
+        return m->n_hit;
+}
+
+unsigned mmap_cache_get_missed(MMapCache *m) {
+        assert(m);
 
-        context_free(c);
+        return m->n_missed;
 }