qemu/osdep: Add excluded fd parameter to qemu_close_all_open_fd()

In order for this function to be usable by tap.c code, add a list of
file descriptors that should not be closed.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Message-ID: <20240802145423.3232974-5-cleger@rivosinc.com>
[rth: Use max_fd in qemu_close_all_open_fd_close_range]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/qemu/osdep.h

@@ -760,9 +760,13 @@ int qemu_fdatasync(int fd);
 /**
  * qemu_close_all_open_fd:
  *
- * Close all open file descriptors
+ * Close all open file descriptors except the ones supplied in the @skip array
+ *
+ * @skip: ordered array of distinct file descriptors that should not be closed
+ *        if any, or NULL.
+ * @nskip: number of entries in the @skip array or 0 if @skip is NULL.
  */
-void qemu_close_all_open_fd(void);
+void qemu_close_all_open_fd(const int *skip, unsigned int nskip);
 
 /**
  * Sync changes made to the memory mapped file back to the backing

system/async-teardown.c

@@ -52,7 +52,7 @@ static int async_teardown_fn(void *arg)
      * Close all file descriptors that might have been inherited from the
      * main qemu process when doing clone, needed to make libvirt happy.
      */
-    qemu_close_all_open_fd();
+    qemu_close_all_open_fd(NULL, 0);
 
     /* Set up a handler for SIGHUP and unblock SIGHUP. */
     sigaction(SIGHUP, &sa, NULL);

util/oslib-posix.c

@@ -808,11 +808,12 @@ int qemu_msync(void *addr, size_t length, int fd)
     return msync(addr, length, MS_SYNC);
 }
 
-static bool qemu_close_all_open_fd_proc(void)
+static bool qemu_close_all_open_fd_proc(const int *skip, unsigned int nskip)
 {
     struct dirent *de;
     int fd, dfd;
     DIR *dir;
+    unsigned int skip_start = 0, skip_end = nskip;
 
     dir = opendir("/proc/self/fd");
     if (!dir) {
@@ -823,8 +824,33 @@ static bool qemu_close_all_open_fd_proc(void)
     dfd = dirfd(dir);
 
     for (de = readdir(dir); de; de = readdir(dir)) {
+        bool close_fd = true;
+
+        if (de->d_name[0] == '.') {
+            continue;
+        }
         fd = atoi(de->d_name);
-        if (fd != dfd) {
+        if (fd == dfd) {
+            continue;
+        }
+
+        for (unsigned int i = skip_start; i < skip_end; i++) {
+            if (fd < skip[i]) {
+                /* We are below the next skipped fd, break */
+                break;
+            } else if (fd == skip[i]) {
+                close_fd = false;
+                /* Restrict the range as we found fds matching start/end */
+                if (i == skip_start) {
+                    skip_start++;
+                } else if (i == skip_end) {
+                    skip_end--;
+                }
+                break;
+            }
+        }
+
+        if (close_fd) {
             close(fd);
         }
     }
@@ -833,24 +859,60 @@ static bool qemu_close_all_open_fd_proc(void)
     return true;
 }
 
-static bool qemu_close_all_open_fd_close_range(void)
+static bool qemu_close_all_open_fd_close_range(const int *skip,
+                                               unsigned int nskip,
+                                               int open_max)
 {
 #ifdef CONFIG_CLOSE_RANGE
-    int r = close_range(0, ~0U, 0);
-    if (!r) {
-        /* Success, no need to try other ways. */
-        return true;
-    }
-#endif
+    int max_fd = open_max - 1;
+    int first = 0, last;
+    unsigned int cur_skip = 0;
+    int ret;
+
+    do {
+        /* Find the start boundary of the range to close */
+        while (cur_skip < nskip && first == skip[cur_skip]) {
+            cur_skip++;
+            first++;
+        }
+
+        /* Find the upper boundary of the range to close */
+        last = max_fd;
+        if (cur_skip < nskip) {
+            last = skip[cur_skip] - 1;
+            last = MIN(last, max_fd);
+        }
+
+        /* With the adjustments to the range, we might be done. */
+        if (first > last) {
+            break;
+        }
+
+        ret = close_range(first, last, 0);
+        if (ret < 0) {
+            return false;
+        }
+
+        first = last + 1;
+    } while (last < max_fd);
+
+    return true;
+#else
     return false;
+#endif
 }
 
-static void qemu_close_all_open_fd_fallback(void)
+static void qemu_close_all_open_fd_fallback(const int *skip, unsigned int nskip,
+                                            int open_max)
 {
-    int open_max = sysconf(_SC_OPEN_MAX), i;
+    unsigned int cur_skip = 0;
 
     /* Fallback */
-    for (i = 0; i < open_max; i++) {
+    for (int i = 0; i < open_max; i++) {
+        if (cur_skip < nskip && i == skip[cur_skip]) {
+            cur_skip++;
+            continue;
+        }
         close(i);
     }
 }
@@ -858,10 +920,14 @@ static void qemu_close_all_open_fd_fallback(void)
 /*
  * Close all open file descriptors.
  */
-void qemu_close_all_open_fd(void)
+void qemu_close_all_open_fd(const int *skip, unsigned int nskip)
 {
-    if (!qemu_close_all_open_fd_close_range() &&
-        !qemu_close_all_open_fd_proc()) {
-        qemu_close_all_open_fd_fallback();
+    int open_max = sysconf(_SC_OPEN_MAX);
+
+    assert(skip != NULL || nskip == 0);
+
+    if (!qemu_close_all_open_fd_close_range(skip, nskip, open_max) &&
+        !qemu_close_all_open_fd_proc(skip, nskip)) {
+        qemu_close_all_open_fd_fallback(skip, nskip, open_max);
     }
 }