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authorTavian Barnes <tavianator@tavianator.com>2023-03-30 12:39:37 -0400
committerTavian Barnes <tavianator@tavianator.com>2023-06-12 14:39:34 -0400
commit0cca5b64e1355af5d2c3d935da4e110982273703 (patch)
tree9cd3600e6db701c823995b284d9c07453cbf0409
parent0c10a1e984bc2bed1fe3a7dadbd94a9c24139a91 (diff)
downloadbfs-0cca5b64e1355af5d2c3d935da4e110982273703.tar.xz
bftw: Implement open file pinning
-rw-r--r--src/bftw.c132
1 files changed, 100 insertions, 32 deletions
diff --git a/src/bftw.c b/src/bftw.c
index a3e8d9b..4a49457 100644
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -51,11 +51,15 @@ struct bftw_file {
/** This file's depth in the walk. */
size_t depth;
- /** Reference count. */
+ /** Reference count (for ->parent). */
size_t refcount;
+ /** Pin count (for ->fd). */
+ size_t pincount;
/** An open descriptor to this file, or -1. */
int fd;
+ /** An open directory for this file, if any. */
+ struct bfs_dir *dir;
/** This file's type, if known. */
enum bfs_type type;
@@ -101,27 +105,58 @@ static void bftw_cache_init(struct bftw_cache *cache, size_t capacity) {
cache->capacity = capacity;
}
-/** Remove a bftw_file from the cache. */
-static void bftw_cache_remove(struct bftw_cache *cache, struct bftw_file *file) {
+/** Remove a bftw_file from the LRU list. */
+static void bftw_lru_remove(struct bftw_cache *cache, struct bftw_file *file) {
if (cache->target == file) {
cache->target = file->lru.prev;
}
LIST_REMOVE(cache, file, lru);
+}
+/** Remove a bftw_file from the cache. */
+static void bftw_cache_remove(struct bftw_cache *cache, struct bftw_file *file) {
+ bftw_lru_remove(cache, file);
++cache->capacity;
}
/** Close a bftw_file. */
static void bftw_file_close(struct bftw_cache *cache, struct bftw_file *file) {
bfs_assert(file->fd >= 0);
+ bfs_assert(file->pincount == 0);
- if (LIST_ATTACHED(cache, file, lru)) {
- bftw_cache_remove(cache, file);
+ if (file->dir) {
+ bfs_assert(file->fd == bfs_dirfd(file->dir));
+ bfs_closedir(file->dir);
+ file->dir = NULL;
+ } else {
+ xclose(file->fd);
}
- xclose(file->fd);
file->fd = -1;
+ bftw_cache_remove(cache, file);
+}
+
+/** Free an open directory. */
+static void bftw_file_freedir(struct bftw_cache *cache, struct bftw_file *file) {
+ if (!file->dir) {
+ return;
+ }
+
+ // Try to keep an open fd if any children exist
+ bool reffed = file->refcount > 1;
+ // Keep the fd the same if it's pinned
+ bool pinned = file->pincount > 0;
+
+ if (reffed || pinned) {
+ int fd = bfs_freedir(file->dir, pinned);
+ if (fd >= 0) {
+ file->fd = fd;
+ file->dir = NULL;
+ }
+ } else {
+ bftw_file_close(cache, file);
+ }
}
/** Pop the least recently used directory from the cache. */
@@ -135,6 +170,18 @@ static int bftw_cache_pop(struct bftw_cache *cache) {
return 0;
}
+/** Add a bftw_file to the LRU list. */
+static void bftw_lru_add(struct bftw_cache *cache, struct bftw_file *file) {
+ bfs_assert(file->fd >= 0);
+
+ LIST_INSERT(cache, cache->target, file, lru);
+
+ // Prefer to keep the root paths open by keeping them at the head of the list
+ if (file->depth == 0) {
+ cache->target = file;
+ }
+}
+
/** Add a bftw_file to the cache. */
static int bftw_cache_add(struct bftw_cache *cache, struct bftw_file *file) {
bfs_assert(file->fd >= 0);
@@ -148,14 +195,28 @@ static int bftw_cache_add(struct bftw_cache *cache, struct bftw_file *file) {
bfs_assert(cache->capacity > 0);
--cache->capacity;
- LIST_INSERT(cache, cache->target, file, lru);
+ bftw_lru_add(cache, file);
+ return 0;
+}
- // Prefer to keep the root paths open by keeping them at the head of the list
- if (file->depth == 0) {
- cache->target = file;
+/** Pin a cache entry so it won't be closed. */
+static void bftw_cache_pin(struct bftw_cache *cache, struct bftw_file *file) {
+ bfs_assert(file->fd >= 0);
+
+ if (file->pincount++ == 0) {
+ bftw_lru_remove(cache, file);
}
+}
- return 0;
+/** Unpin a cache entry. */
+static void bftw_cache_unpin(struct bftw_cache *cache, struct bftw_file *file) {
+ bfs_assert(file->fd >= 0);
+ bfs_assert(file->pincount > 0);
+
+ if (--file->pincount == 0) {
+ bftw_lru_add(cache, file);
+ bftw_file_freedir(cache, file);
+ }
}
/** Compute the name offset of a child path. */
@@ -201,7 +262,9 @@ static struct bftw_file *bftw_file_new(struct bftw_file *parent, const char *nam
file->lru.prev = file->lru.next = NULL;
file->refcount = 1;
+ file->pincount = 0;
file->fd = -1;
+ file->dir = NULL;
file->type = BFS_UNKNOWN;
file->dev = -1;
@@ -234,8 +297,7 @@ static int bftw_file_openat(struct bftw_cache *cache, struct bftw_file *file, st
int at_fd = AT_FDCWD;
if (base) {
- // Remove base from the cache temporarily so it stays open
- bftw_cache_remove(cache, base);
+ bftw_cache_pin(cache, base);
at_fd = base->fd;
}
@@ -250,7 +312,7 @@ static int bftw_file_openat(struct bftw_cache *cache, struct bftw_file *file, st
}
if (base) {
- bftw_cache_add(cache, base);
+ bftw_cache_unpin(cache, base);
}
if (fd >= 0) {
@@ -309,6 +371,19 @@ static int bftw_file_open(struct bftw_cache *cache, struct bftw_file *file, cons
}
/**
+ * Associate an open directory with a bftw_file.
+ */
+static void bftw_file_set_dir(struct bftw_cache *cache, struct bftw_file *file, struct bfs_dir *dir) {
+ bfs_assert(!file->dir);
+ file->dir = dir;
+
+ if (file->fd < 0) {
+ file->fd = bfs_dirfd(dir);
+ bftw_cache_add(cache, file);
+ }
+}
+
+/**
* Open a bftw_file as a directory.
*
* @param cache
@@ -326,7 +401,11 @@ static struct bfs_dir *bftw_file_opendir(struct bftw_cache *cache, struct bftw_f
return NULL;
}
- return bfs_opendir(fd, NULL);
+ struct bfs_dir *dir = bfs_opendir(fd, NULL);
+ if (dir) {
+ bftw_file_set_dir(cache, file, dir);
+ }
+ return dir;
}
/** Free a bftw_file. */
@@ -798,7 +877,9 @@ static int bftw_opendir(struct bftw_state *state) {
}
state->dir = bftw_file_opendir(&state->cache, state->file, state->path);
- if (!state->dir) {
+ if (state->dir) {
+ bftw_cache_pin(&state->cache, state->file);
+ } else {
state->direrror = errno;
}
return 0;
@@ -848,22 +929,9 @@ static int bftw_gc(struct bftw_state *state, enum bftw_gc_flags flags) {
int ret = 0;
if (state->dir) {
- struct bftw_file *file = state->file;
- bfs_assert(file && file->fd >= 0);
-
- if (file->refcount > 1) {
- // Keep the fd around if any subdirectories exist
- file->fd = bfs_freedir(state->dir, false);
- } else {
- file->fd = -1;
- }
-
- if (file->fd < 0) {
- bfs_closedir(state->dir);
- bftw_cache_remove(&state->cache, file);
- }
+ bftw_cache_unpin(&state->cache, state->file);
+ bftw_file_freedir(&state->cache, state->file);
}
-
state->dir = NULL;
state->de = NULL;
@@ -876,8 +944,8 @@ static int bftw_gc(struct bftw_state *state, enum bftw_gc_flags flags) {
} else {
state->error = state->direrror;
}
- state->direrror = 0;
}
+ state->direrror = 0;
enum bftw_gc_flags visit = BFTW_VISIT_FILE;
while (state->file) {