git/compat/win32/fscache.c

#include "../../git-compat-util.h"
#include "../../hashmap.h"
#include "../win32.h"
#include "fscache.h"
#include "../../dir.h"
#include "../../abspath.h"
#include "../../trace.h"
#include "config.h"

static int initialized;
static volatile long enabled;
static struct hashmap map;
static CRITICAL_SECTION mutex;
static unsigned int lstat_requests;
static unsigned int opendir_requests;
static unsigned int fscache_requests;
static unsigned int fscache_misses;
static struct trace_key trace_fscache = TRACE_KEY_INIT(FSCACHE);

/*
 * An entry in the file system cache. Used for both entire directory listings
 * and file entries.
 */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic"
struct fsentry {
	struct hashmap_entry ent;
	mode_t st_mode;
	/* Pointer to the directory listing, or NULL for the listing itself. */
	struct fsentry *list;
	/* Pointer to the next file entry of the list. */
	struct fsentry *next;

	union {
		/* Reference count of the directory listing. */
		volatile long refcnt;
		/* Handle to wait on the loading thread. */
		HANDLE hwait;
		struct {
			/* More stat members (only used for file entries). */
			off64_t st_size;
			struct timespec st_atim;
			struct timespec st_mtim;
			struct timespec st_ctim;
		} s;
	} u;

	/* Length of name. */
	unsigned short len;
	/*
	 * Name of the entry. For directory listings: relative path of the
	 * directory, without trailing '/' (empty for cwd()). For file entries:
	 * name of the file. Typically points to the end of the structure if
	 * the fsentry is allocated on the heap (see fsentry_alloc), or to a
	 * local variable if on the stack (see fsentry_init).
	 */
	struct dirent dirent;
};
#pragma GCC diagnostic pop

#pragma GCC diagnostic push
#ifdef __clang__
#pragma GCC diagnostic ignored "-Wflexible-array-extensions"
#endif
struct heap_fsentry {
	union {
		struct fsentry ent;
		char dummy[sizeof(struct fsentry) + MAX_PATH];
	} u;
};
#pragma GCC diagnostic pop

/*
 * Compares the paths of two fsentry structures for equality.
 */
static int fsentry_cmp(void *cmp_data UNUSED,
		       const struct fsentry *fse1, const struct fsentry *fse2,
		       void *keydata UNUSED)
{
	int res;
	if (fse1 == fse2)
		return 0;

	/* compare the list parts first */
	if (fse1->list != fse2->list &&
	    (res = fsentry_cmp(NULL, fse1->list ? fse1->list : fse1,
			       fse2->list ? fse2->list	: fse2, NULL)))
		return res;

	/* if list parts are equal, compare len and name */
	if (fse1->len != fse2->len)
		return fse1->len - fse2->len;
	return fspathncmp(fse1->dirent.d_name, fse2->dirent.d_name, fse1->len);
}

/*
 * Calculates the hash code of an fsentry structure's path.
 */
static unsigned int fsentry_hash(const struct fsentry *fse)
{
	unsigned int hash = fse->list ? fse->list->ent.hash : 0;
	return hash ^ memihash(fse->dirent.d_name, fse->len);
}

/*
 * Initialize an fsentry structure for use by fsentry_hash and fsentry_cmp.
 */
static void fsentry_init(struct fsentry *fse, struct fsentry *list,
			 const char *name, size_t len)
{
	fse->list = list;
	if (len > MAX_PATH)
		BUG("Trying to allocate fsentry for long path '%.*s'",
		    (int)len, name);
	memcpy(fse->dirent.d_name, name, len);
	fse->dirent.d_name[len] = 0;
	fse->len = len;
	hashmap_entry_init(&fse->ent, fsentry_hash(fse));
}

/*
 * Allocate an fsentry structure on the heap.
 */
static struct fsentry *fsentry_alloc(struct fsentry *list, const char *name,
		size_t len)
{
	/* overallocate fsentry and copy the name to the end */
	struct fsentry *fse = xmalloc(sizeof(struct fsentry) + len + 1);
	/* init the rest of the structure */
	fsentry_init(fse, list, name, len);
	fse->next = NULL;
	fse->u.refcnt = 1;
	return fse;
}

/*
 * Add a reference to an fsentry.
 */
inline static void fsentry_addref(struct fsentry *fse)
{
	if (fse->list)
		fse = fse->list;

	InterlockedIncrement(&(fse->u.refcnt));
}

/*
 * Release the reference to an fsentry, frees the memory if its the last ref.
 */
static void fsentry_release(struct fsentry *fse)
{
	if (fse->list)
		fse = fse->list;

	if (InterlockedDecrement(&(fse->u.refcnt)))
		return;

	while (fse) {
		struct fsentry *next = fse->next;
		free(fse);
		fse = next;
	}
}

/*
 * Allocate and initialize an fsentry from a WIN32_FIND_DATA structure.
 */
static struct fsentry *fseentry_create_entry(struct fsentry *list,
					     const WIN32_FIND_DATAW *fdata)
{
	char buf[MAX_PATH * 3];
	int len;
	struct fsentry *fse;
	len = xwcstoutf(buf, fdata->cFileName, ARRAY_SIZE(buf));

	fse = fsentry_alloc(list, buf, len);

	fse->st_mode = file_attr_to_st_mode(fdata->FileAttributes,
					    fdata->EaSize);
	fse->dirent.d_type = S_ISREG(fse->st_mode) ? DT_REG :
			S_ISDIR(fse->st_mode) ? DT_DIR : DT_LNK;
	fse->u.s.st_size = (((off64_t) (fdata->nFileSizeHigh)) << 32)
			| fdata->nFileSizeLow;
	filetime_to_timespec(&(fdata->ftLastAccessTime), &(fse->u.s.st_atim));
	filetime_to_timespec(&(fdata->ftLastWriteTime), &(fse->u.s.st_mtim));
	filetime_to_timespec(&(fdata->ftCreationTime), &(fse->u.s.st_ctim));

	return fse;
}

/*
 * Create an fsentry-based directory listing (similar to opendir / readdir).
 * Dir should not contain trailing '/'. Use an empty string for the current
 * directory (not "."!).
 */
static struct fsentry *fsentry_create_list(const struct fsentry *dir,
					   int *dir_not_found)
{
	wchar_t pattern[MAX_PATH + 2]; /* + 2 for '/' '*' */
	WIN32_FIND_DATAW fdata;
	HANDLE h;
	int wlen;
	struct fsentry *list, **phead;
	DWORD err;

	*dir_not_found = 0;

	/* convert name to UTF-16 and check length < MAX_PATH */
	if ((wlen = xutftowcsn(pattern, dir->dirent.d_name, MAX_PATH,
			       dir->len)) < 0) {
		if (errno == ERANGE)
			errno = ENAMETOOLONG;
		return NULL;
	}

	/* append optional '/' and wildcard '*' */
	if (wlen)
		pattern[wlen++] = '/';
	pattern[wlen++] = '*';
	pattern[wlen] = 0;

	/* open find handle */
	h = FindFirstFileExW(pattern, FindExInfoBasic, &fdata, FindExSearchNameMatch,
		NULL, FIND_FIRST_EX_LARGE_FETCH);
	if (h == INVALID_HANDLE_VALUE) {
		err = GetLastError();
		*dir_not_found = 1; /* or empty directory */
		errno = (err == ERROR_DIRECTORY) ? ENOTDIR : err_win_to_posix(err);
		trace_printf_key(&trace_fscache, "fscache: error(%d) '%s'\n",
						 errno, dir->dirent.d_name);
		return NULL;
	}

	/* allocate object to hold directory listing */
	list = fsentry_alloc(NULL, dir->dirent.d_name, dir->len);
	list->st_mode = S_IFDIR;
	list->dirent.d_type = DT_DIR;

	/* walk directory and build linked list of fsentry structures */
	phead = &list->next;
	do {
		*phead = fseentry_create_entry(list, &fdata);
		phead = &(*phead)->next;
	} while (FindNextFileW(h, &fdata));

	/* remember result of last FindNextFile, then close find handle */
	err = GetLastError();
	FindClose(h);

	/* return the list if we've got all the files */
	if (err == ERROR_NO_MORE_FILES)
		return list;

	/* otherwise free the list and return error */
	fsentry_release(list);
	errno = err_win_to_posix(err);
	return NULL;
}

/*
 * Adds a directory listing to the cache.
 */
static void fscache_add(struct fsentry *fse)
{
	if (fse->list)
		fse = fse->list;

	for (; fse; fse = fse->next)
		hashmap_add(&map, &fse->ent);
}

/*
 * Clears the cache.
 */
static void fscache_clear(void)
{
	hashmap_clear_and_free(&map, struct fsentry, ent);
	hashmap_init(&map, (hashmap_cmp_fn)fsentry_cmp, NULL, 0);
	lstat_requests = opendir_requests = 0;
	fscache_misses = fscache_requests = 0;
}

/*
 * Checks if the cache is enabled for the given path.
 */
int fscache_enabled(const char *path)
{
	return enabled > 0 && !is_absolute_path(path);
}

/*
 * Looks up a cache entry, waits if its being loaded by another thread.
 * The mutex must be owned by the calling thread.
 */
static struct fsentry *fscache_get_wait(struct fsentry *key)
{
	struct fsentry *fse = hashmap_get_entry(&map, key, ent, NULL);

	/* return if its a 'real' entry (future entries have refcnt == 0) */
	if (!fse || fse->list || fse->u.refcnt)
		return fse;

	/* create an event and link our key to the future entry */
	key->u.hwait = CreateEvent(NULL, TRUE, FALSE, NULL);
	key->next = fse->next;
	fse->next = key;

	/* wait for the loading thread to signal us */
	LeaveCriticalSection(&mutex);
	WaitForSingleObject(key->u.hwait, INFINITE);
	CloseHandle(key->u.hwait);
	EnterCriticalSection(&mutex);

	/* repeat cache lookup */
	return hashmap_get_entry(&map, key, ent, NULL);
}

/*
 * Looks up or creates a cache entry for the specified key.
 */
static struct fsentry *fscache_get(struct fsentry *key)
{
	struct fsentry *fse, *future, *waiter;
	int dir_not_found;

	EnterCriticalSection(&mutex);
	fscache_requests++;
	/* check if entry is in cache */
	fse = fscache_get_wait(key);
	if (fse) {
		if (fse->st_mode)
			fsentry_addref(fse);
		else
			fse = NULL; /* non-existing directory */
		LeaveCriticalSection(&mutex);
		return fse;
	}
	/* if looking for a file, check if directory listing is in cache */
	if (!fse && key->list) {
		fse = fscache_get_wait(key->list);
		if (fse) {
			LeaveCriticalSection(&mutex);
			/*
			 * dir entry without file entry, or dir does not
			 * exist -> file doesn't exist
			 */
			errno = ENOENT;
			return NULL;
		}
	}

	/* add future entry to indicate that we're loading it */
	future = key->list ? key->list : key;
	future->next = NULL;
	future->u.refcnt = 0;
	hashmap_add(&map, &future->ent);

	/* create the directory listing (outside mutex!) */
	LeaveCriticalSection(&mutex);
	fse = fsentry_create_list(future, &dir_not_found);
	EnterCriticalSection(&mutex);

	/* remove future entry and signal waiting threads */
	hashmap_remove(&map, &future->ent, NULL);
	waiter = future->next;
	while (waiter) {
		HANDLE h = waiter->u.hwait;
		waiter = waiter->next;
		SetEvent(h);
	}

	/* leave on error (errno set by fsentry_create_list) */
	if (!fse) {
		if (dir_not_found && key->list) {
			/*
			 * Record that the directory does not exist (or is
			 * empty, which for all practical matters is the same
			 * thing as far as fscache is concerned).
			 */
			fse = fsentry_alloc(key->list->list,
					    key->list->dirent.d_name,
					    key->list->len);
			fse->st_mode = 0;
			hashmap_add(&map, &fse->ent);
		}
		LeaveCriticalSection(&mutex);
		return NULL;
	}

	/* add directory listing to the cache */
	fscache_misses++;
	fscache_add(fse);

	/* lookup file entry if requested (fse already points to directory) */
	if (key->list)
		fse = hashmap_get_entry(&map, key, ent, NULL);

	if (fse && !fse->st_mode)
		fse = NULL; /* non-existing directory */

	/* return entry or ENOENT */
	if (fse)
		fsentry_addref(fse);
	else
		errno = ENOENT;

	LeaveCriticalSection(&mutex);
	return fse;
}

/*
 * Enables or disables the cache. Note that the cache is read-only, changes to
 * the working directory are NOT reflected in the cache while enabled.
 */
int fscache_enable(int enable, size_t initial_size)
{
	int result;

	if (!initialized) {
		int fscache = git_env_bool("GIT_TEST_FSCACHE", -1);

		/* allow the cache to be disabled entirely */
		if (fscache != -1)
			core_fscache = fscache;
		if (!core_fscache)
			return 0;

		InitializeCriticalSection(&mutex);
		lstat_requests = opendir_requests = 0;
		fscache_misses = fscache_requests = 0;
		/*
		 * avoid having to rehash by leaving room for the parent dirs.
		 * '4' was determined empirically by testing several repos
		 */
		hashmap_init(&map, (hashmap_cmp_fn) fsentry_cmp, NULL, initial_size * 4);
		initialized = 1;
	}

	result = enable ? InterlockedIncrement(&enabled)
			: InterlockedDecrement(&enabled);

	if (enable && result == 1) {
		/* redirect opendir and lstat to the fscache implementations */
		opendir = fscache_opendir;
		lstat = fscache_lstat;
	} else if (!enable && !result) {
		/* reset opendir and lstat to the original implementations */
		opendir = dirent_opendir;
		lstat = mingw_lstat;
		EnterCriticalSection(&mutex);
		trace_printf_key(&trace_fscache, "fscache: lstat %u, opendir %u, "
						 "total requests/misses %u/%u\n",
				lstat_requests, opendir_requests,
				fscache_requests, fscache_misses);
		fscache_clear();
		LeaveCriticalSection(&mutex);
	}
	trace_printf_key(&trace_fscache, "fscache: enable(%d)\n", enable);
	return result;
}

/*
 * Flush cached stats result when fscache is enabled.
 */
void fscache_flush(void)
{
	if (enabled) {
		EnterCriticalSection(&mutex);
		fscache_clear();
		LeaveCriticalSection(&mutex);
	}
}

/*
 * Lstat replacement, uses the cache if enabled, otherwise redirects to
 * mingw_lstat.
 */
int fscache_lstat(const char *filename, struct stat *st)
{
	int dirlen, base, len;
#pragma GCC diagnostic push
#ifdef __clang__
#pragma GCC diagnostic ignored "-Wflexible-array-extensions"
#endif
	struct heap_fsentry key[2];
#pragma GCC diagnostic pop
	struct fsentry *fse;

	if (!fscache_enabled(filename))
		return mingw_lstat(filename, st);

	lstat_requests++;
	/* split filename into path + name */
	len = strlen(filename);
	if (len && is_dir_sep(filename[len - 1]))
		len--;
	base = len;
	while (base && !is_dir_sep(filename[base - 1]))
		base--;
	dirlen = base ? base - 1 : 0;

	/* lookup entry for path + name in cache */
	fsentry_init(&key[0].u.ent, NULL, filename, dirlen);
	fsentry_init(&key[1].u.ent, &key[0].u.ent, filename + base, len - base);
	fse = fscache_get(&key[1].u.ent);
	if (!fse) {
		errno = ENOENT;
		return -1;
	}

	/*
	 * Special case symbolic links: FindFirstFile()/FindNextFile() did not
	 * provide us with the length of the target path.
	 */
	if (fse->u.s.st_size == MAX_PATH && S_ISLNK(fse->st_mode)) {
		char buf[MAX_LONG_PATH];
		int len = readlink(filename, buf, sizeof(buf) - 1);

		if (len > 0)
			fse->u.s.st_size = len;
	}

	/* copy stat data */
	st->st_ino = 0;
	st->st_gid = 0;
	st->st_uid = 0;
	st->st_dev = 0;
	st->st_rdev = 0;
	st->st_nlink = 1;
	st->st_mode = fse->st_mode;
	st->st_size = fse->u.s.st_size;
	st->st_atim = fse->u.s.st_atim;
	st->st_mtim = fse->u.s.st_mtim;
	st->st_ctim = fse->u.s.st_ctim;

	/* don't forget to release fsentry */
	fsentry_release(fse);
	return 0;
}

typedef struct fscache_DIR {
	struct DIR base_dir; /* extend base struct DIR */
	struct fsentry *pfsentry;
	struct dirent *dirent;
} fscache_DIR;

/*
 * Readdir replacement.
 */
static struct dirent *fscache_readdir(DIR *base_dir)
{
	fscache_DIR *dir = (fscache_DIR*) base_dir;
	struct fsentry *next = dir->pfsentry->next;
	if (!next)
		return NULL;
	dir->pfsentry = next;
	dir->dirent = &next->dirent;
	return dir->dirent;
}

/*
 * Closedir replacement.
 */
static int fscache_closedir(DIR *base_dir)
{
	fscache_DIR *dir = (fscache_DIR*) base_dir;
	fsentry_release(dir->pfsentry);
	free(dir);
	return 0;
}

/*
 * Opendir replacement, uses a directory listing from the cache if enabled,
 * otherwise calls original dirent implementation.
 */
DIR *fscache_opendir(const char *dirname)
{
	struct heap_fsentry key;
	struct fsentry *list;
	fscache_DIR *dir;
	int len;

	if (!fscache_enabled(dirname))
		return dirent_opendir(dirname);

	opendir_requests++;
	/* prepare name (strip trailing '/', replace '.') */
	len = strlen(dirname);
	if ((len == 1 && dirname[0] == '.') ||
	    (len && is_dir_sep(dirname[len - 1])))
		len--;

	/* get directory listing from cache */
	fsentry_init(&key.u.ent, NULL, dirname, len);
	list = fscache_get(&key.u.ent);
	if (!list)
		return NULL;

	/* alloc and return DIR structure */
	dir = (fscache_DIR*) xmalloc(sizeof(fscache_DIR));
	dir->base_dir.preaddir = fscache_readdir;
	dir->base_dir.pclosedir = fscache_closedir;
	dir->pfsentry = list;
	return (DIR*) dir;
}