[PATCH v4 4/6] util/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>

---

Changes in v4:
- add 'first > last' check logic
- reorder the ifdefs logic
- change i to unsigned int type
- use qemu_strtoi() instead of atoi()
- limit last upper value to sysconf(_SC_OPEN_MAX) - 1

Changes in v3:
- fix win32 build failure

Changes in v2:
- new patch: "util/osdep: Introduce qemu_close_range()"

 include/qemu/osdep.h |  1 +
 util/osdep.c         | 60 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 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..1d8c719b3f 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -411,6 +411,66 @@ int qemu_close(int fd)
     return close(fd);
 }
 
+int qemu_close_range(unsigned int first, unsigned int last)
+{
+    if (first > last) {
+        errno = EINVAL;
+        return -1;
+    }
+
+#ifndef _WIN32
+    if (last >= sysconf(_SC_OPEN_MAX)) {
+        last = sysconf(_SC_OPEN_MAX) - 1;
+    }
+#endif
+
+#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 *dir = opendir("/proc/self/fd");
+    if (dir) {
+        /* Avoid closing the directory */
+        int dfd = dirfd(dir);
+
+        for (struct dirent *de = readdir(dir); de; de = readdir(dir)) {
+            int fd, ret;
+
+            ret = qemu_strtoi(de->d_name, NULL, 10, &fd);
+            if (ret) {
+                /* skip "." and ".." */
+                continue;
+            }
+            if (fd < first || fd > last) {
+                /* Exclude the fds outside the target range */
+                continue;
+            }
+            if (fd != dfd) {
+                close(fd);
+            }
+        }
+        closedir(dir);
+
+        return 0;
+    }
+#endif
+
+    /*
+     * If /proc is not mounted or /proc/self/fd is not supported,
+     * try close() from first to last.
+     */
+    for (unsigned int i = first; i <= last; i++) {
+        close(i);
+    }
+
+    return 0;
+}
+
 /*
  * Delete a file from the filesystem, unless the filename is /dev/fdset/...
  *
-- 
2.34.1