[PATCH v2 4/6] utils/osdep: Introduce qemu_close_range()

[Bin Meng]

This introduces a new QEMU API qemu_close_range() that closes all
open file descriptors from first to last (included).

This API will try a more efficient call to close_range(), or walk
through of /proc/self/fd whenever these are possible, otherwise it
falls back to a plain close loop.

Co-developed-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Bin Meng <bmeng@tinylab.org>
---

(no changes since v1)

 include/qemu/osdep.h |  1 +
 util/osdep.c         | 47 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index cc61b00ba9..e22434ce10 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -560,6 +560,7 @@ int qemu_open_old(const char *name, int flags, ...);
 int qemu_open(const char *name, int flags, Error **errp);
 int qemu_create(const char *name, int flags, mode_t mode, Error **errp);
 int qemu_close(int fd);
+int qemu_close_range(unsigned int first, unsigned int last);
 int qemu_unlink(const char *name);
 #ifndef _WIN32
 int qemu_dup_flags(int fd, int flags);
diff --git a/util/osdep.c b/util/osdep.c
index e996c4744a..fd7dd2dbdf 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -411,6 +411,53 @@ int qemu_close(int fd)
     return close(fd);
 }
 
+int qemu_close_range(unsigned int first, unsigned int last)
+{
+    DIR *dir = NULL;
+
+#ifdef CONFIG_CLOSE_RANGE
+    int r = close_range(first, last, 0);
+    if (!r) {
+        /* Success, no need to try other ways. */
+        return 0;
+    }
+#endif
+
+#ifdef __linux__
+    dir = opendir("/proc/self/fd");
+#endif
+    if (!dir) {
+        /*
+         * If /proc is not mounted or /proc/self/fd is not supported,
+         * try close() from first to last.
+         */
+        for (int i = first; i <= last; i++) {
+            close(i);
+        }
+
+        return 0;
+    }
+
+#ifndef _WIN32
+    /* Avoid closing the directory */
+    int dfd = dirfd(dir);
+
+    for (struct dirent *de = readdir(dir); de; de = readdir(dir)) {
+        int fd = atoi(de->d_name);
+        if (fd < first || fd > last) {
+            /* Exclude the fds outside the target range */
+            continue;
+        }
+        if (fd != dfd) {
+            close(fd);
+        }
+    }
+    closedir(dir);
+#endif /* _WIN32 */
+
+    return 0;
+}
+
 /*
  * Delete a file from the filesystem, unless the filename is /dev/fdset/...
  *
-- 
2.34.1