tools lib api: Add io_dir an allocation free readdir alternative

glibc's opendir allocates a minimum of 32kb, when called recursively
for a directory tree the memory consumption can add up - nearly 300kb
during perf start-up when processing modules. Add a stack allocated
variant of readdir sized a little more than 1kb.

As getdents64 may be missing from libc, add support using syscall. As
the system call number maybe missing, add #defines for those.

Note, an earlier version of this patch had a feature test for
getdents64 but there were problems on certains distros where
getdents64 would be #define renamed to getdents breaking the code. The
syscall use was made uncondtional to work around this. There is
context in:
https://lore.kernel.org/lkml/20231207050433.1426834-1-irogers@google.com/

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250222061015.303622-2-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

diff --git a/tools/lib/api/Makefile b/tools/lib/api/Makefile
index 7f6396087b467dbad80eafdcdee64718cebda727..8665c799e0fa7155016e8bc6968ebe76a90e1d13 100644 (file)
--- a/tools/lib/api/Makefile
+++ b/tools/lib/api/Makefile
@@ -95,7 +95,7 @@ install_lib: $(LIBFILE)
                $(call do_install_mkdir,$(libdir_SQ)); \
                cp -fpR $(LIBFILE) $(DESTDIR)$(libdir_SQ)
 
-HDRS := cpu.h debug.h io.h
+HDRS := cpu.h debug.h io.h io_dir.h
 FD_HDRS := fd/array.h
 FS_HDRS := fs/fs.h fs/tracing_path.h
 INSTALL_HDRS_PFX := $(DESTDIR)$(prefix)/include/api

diff --git a/tools/lib/api/io_dir.h b/tools/lib/api/io_dir.h
new file mode 100644 (file)
index 0000000..aab7339
--- /dev/null
+++ b/tools/lib/api/io_dir.h
@@ -0,0 +1,104 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+/*
+ * Lightweight directory reading library.
+ */
+#ifndef __API_IO_DIR__
+#define __API_IO_DIR__
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+
+#if !defined(SYS_getdents64)
+#if defined(__x86_64__) || defined(__arm__)
+  #define SYS_getdents64 217
+#elif defined(__i386__) || defined(__s390x__) || defined(__sh__)
+  #define SYS_getdents64 220
+#elif defined(__alpha__)
+  #define SYS_getdents64 377
+#elif defined(__mips__)
+  #define SYS_getdents64 308
+#elif defined(__powerpc64__) || defined(__powerpc__)
+  #define SYS_getdents64 202
+#elif defined(__sparc64__) || defined(__sparc__)
+  #define SYS_getdents64 154
+#elif defined(__xtensa__)
+  #define SYS_getdents64 60
+#else
+  #define SYS_getdents64 61
+#endif
+#endif /* !defined(SYS_getdents64) */
+
+static inline ssize_t perf_getdents64(int fd, void *dirp, size_t count)
+{
+#ifdef MEMORY_SANITIZER
+       memset(dirp, 0, count);
+#endif
+       return syscall(SYS_getdents64, fd, dirp, count);
+}
+
+struct io_dirent64 {
+       ino64_t        d_ino;    /* 64-bit inode number */
+       off64_t        d_off;    /* 64-bit offset to next structure */
+       unsigned short d_reclen; /* Size of this dirent */
+       unsigned char  d_type;   /* File type */
+       char           d_name[NAME_MAX + 1]; /* Filename (null-terminated) */
+};
+
+struct io_dir {
+       int dirfd;
+       ssize_t available_bytes;
+       struct io_dirent64 *next;
+       struct io_dirent64 buff[4];
+};
+
+static inline void io_dir__init(struct io_dir *iod, int dirfd)
+{
+       iod->dirfd = dirfd;
+       iod->available_bytes = 0;
+}
+
+static inline void io_dir__rewinddir(struct io_dir *iod)
+{
+       lseek(iod->dirfd, 0, SEEK_SET);
+       iod->available_bytes = 0;
+}
+
+static inline struct io_dirent64 *io_dir__readdir(struct io_dir *iod)
+{
+       struct io_dirent64 *entry;
+
+       if (iod->available_bytes <= 0) {
+               ssize_t rc = perf_getdents64(iod->dirfd, iod->buff, sizeof(iod->buff));
+
+               if (rc <= 0)
+                       return NULL;
+               iod->available_bytes = rc;
+               iod->next = iod->buff;
+       }
+       entry = iod->next;
+       iod->next = (struct io_dirent64 *)((char *)entry + entry->d_reclen);
+       iod->available_bytes -= entry->d_reclen;
+       return entry;
+}
+
+static inline bool io_dir__is_dir(const struct io_dir *iod, struct io_dirent64 *dent)
+{
+       if (dent->d_type == DT_UNKNOWN) {
+               struct stat st;
+
+               if (fstatat(iod->dirfd, dent->d_name, &st, /*flags=*/0))
+                       return false;
+
+               if (S_ISDIR(st.st_mode)) {
+                       dent->d_type = DT_DIR;
+                       return true;
+               }
+       }
+       return dent->d_type == DT_DIR;
+}
+
+#endif  /* __API_IO_DIR__ */