[PATCH 07/16] qga: flatten safe_open_or_create()

[marcandre.lureau@redhat.com]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

There is a bit too much branching in the function, this can be
simplified a bit, and have a common exit point thanks to ERRP_PROPAGATE.

This also helps with the following error handling changes.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 qga/commands-posix.c | 126 ++++++++++++++++++++++---------------------
 1 file changed, 65 insertions(+), 61 deletions(-)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 69f209af87e6..98d481a58485 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -339,73 +339,77 @@ find_open_flag(const char *mode_str, Error **errp)
 static FILE *
 safe_open_or_create(const char *path, const char *mode, Error **errp)
 {
-    Error *local_err = NULL;
-    int oflag;
-
-    oflag = find_open_flag(mode, &local_err);
-    if (local_err == NULL) {
-        int fd;
+    ERRP_GUARD();
+    int oflag, fd = -1;
+    FILE *f = NULL;
+
+    oflag = find_open_flag(mode, errp);
+    if (*errp) {
+        goto end;
+    }
+
+    /* If the caller wants / allows creation of a new file, we implement it
+     * with a two step process: open() + (open() / fchmod()).
+     *
+     * First we insist on creating the file exclusively as a new file. If
+     * that succeeds, we're free to set any file-mode bits on it. (The
+     * motivation is that we want to set those file-mode bits independently
+     * of the current umask.)
+     *
+     * If the exclusive creation fails because the file already exists
+     * (EEXIST is not possible for any other reason), we just attempt to
+     * open the file, but in this case we won't be allowed to change the
+     * file-mode bits on the preexistent file.
+     *
+     * The pathname should never disappear between the two open()s in
+     * practice. If it happens, then someone very likely tried to race us.
+     * In this case just go ahead and report the ENOENT from the second
+     * open() to the caller.
+     *
+     * If the caller wants to open a preexistent file, then the first
+     * open() is decisive and its third argument is ignored, and the second
+     * open() and the fchmod() are never called.
+     */
+    fd = open(path, oflag | ((oflag & O_CREAT) ? O_EXCL : 0), 0);
+    if (fd == -1 && errno == EEXIST) {
+        oflag &= ~(unsigned)O_CREAT;
+        fd = open(path, oflag);
+    }
+    if (fd == -1) {
+        error_setg_errno(errp, errno,
+                         "failed to open file '%s' "
+                         "(mode: '%s')",
+                         path, mode);
+        goto end;
+    }
 
-        /* If the caller wants / allows creation of a new file, we implement it
-         * with a two step process: open() + (open() / fchmod()).
-         *
-         * First we insist on creating the file exclusively as a new file. If
-         * that succeeds, we're free to set any file-mode bits on it. (The
-         * motivation is that we want to set those file-mode bits independently
-         * of the current umask.)
-         *
-         * If the exclusive creation fails because the file already exists
-         * (EEXIST is not possible for any other reason), we just attempt to
-         * open the file, but in this case we won't be allowed to change the
-         * file-mode bits on the preexistent file.
-         *
-         * The pathname should never disappear between the two open()s in
-         * practice. If it happens, then someone very likely tried to race us.
-         * In this case just go ahead and report the ENOENT from the second
-         * open() to the caller.
-         *
-         * If the caller wants to open a preexistent file, then the first
-         * open() is decisive and its third argument is ignored, and the second
-         * open() and the fchmod() are never called.
-         */
-        fd = open(path, oflag | ((oflag & O_CREAT) ? O_EXCL : 0), 0);
-        if (fd == -1 && errno == EEXIST) {
-            oflag &= ~(unsigned)O_CREAT;
-            fd = open(path, oflag);
-        }
+    qemu_set_cloexec(fd);
 
-        if (fd == -1) {
-            error_setg_errno(&local_err, errno, "failed to open file '%s' "
-                             "(mode: '%s')", path, mode);
-        } else {
-            qemu_set_cloexec(fd);
+    if ((oflag & O_CREAT) && fchmod(fd, DEFAULT_NEW_FILE_MODE) == -1) {
+        error_setg_errno(errp, errno,
+                         "failed to set permission "
+                         "0%03o on new file '%s' (mode: '%s')",
+                         (unsigned)DEFAULT_NEW_FILE_MODE, path, mode);
+        goto end;
+    }
 
-            if ((oflag & O_CREAT) && fchmod(fd, DEFAULT_NEW_FILE_MODE) == -1) {
-                error_setg_errno(&local_err, errno, "failed to set permission "
-                                 "0%03o on new file '%s' (mode: '%s')",
-                                 (unsigned)DEFAULT_NEW_FILE_MODE, path, mode);
-            } else {
-                FILE *f;
-
-                f = fdopen(fd, mode);
-                if (f == NULL) {
-                    error_setg_errno(&local_err, errno, "failed to associate "
-                                     "stdio stream with file descriptor %d, "
-                                     "file '%s' (mode: '%s')", fd, path, mode);
-                } else {
-                    return f;
-                }
-            }
+    f = fdopen(fd, mode);
+    if (f == NULL) {
+        error_setg_errno(errp, errno,
+                         "failed to associate "
+                         "stdio stream with file descriptor %d, "
+                         "file '%s' (mode: '%s')",
+                         fd, path, mode);
+    }
 
-            close(fd);
-            if (oflag & O_CREAT) {
-                unlink(path);
-            }
+end:
+    if (f == NULL && fd != -1) {
+        close(fd);
+        if (oflag & O_CREAT) {
+            unlink(path);
         }
     }
-
-    error_propagate(errp, local_err);
-    return NULL;
+    return f;
 }
 
 int64_t qmp_guest_file_open(const char *path, bool has_mode, const char *mode,
-- 
2.36.0.44.g0f828332d5ac