Merge remote-tracking branch 'remotes/berrange/tags/block-odirect-pull-request' into staging

block: improve error reporting for unsupported O_DIRECT

# gpg: Signature made Wed 16 Sep 2020 10:45:48 BST
# gpg:                using RSA key DAF3A6FDB26B62912D0E8E3FBE86EBB415104FDF
# gpg: Good signature from "Daniel P. Berrange <dan@berrange.com>" [full]
# gpg:                 aka "Daniel P. Berrange <berrange@redhat.com>" [full]
# Primary key fingerprint: DAF3 A6FD B26B 6291 2D0E  8E3F BE86 EBB4 1510 4FDF

* remotes/berrange/tags/block-odirect-pull-request:
  block/file: switch to use qemu_open/qemu_create for improved errors
  util: give a specific error message when O_DIRECT doesn't work
  util: introduce qemu_open and qemu_create with error reporting
  util: add Error object for qemu_open_internal error reporting
  util: refactor qemu_open_old to split off variadic args handling
  util: rename qemu_open() to qemu_open_old()
  util: split off a helper for dealing with O_CLOEXEC flag
  monitor: simplify functions for getting a dup'd fdset entry

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 75 insertions, 31 deletions

diff --git a/util/osdep.c b/util/osdep.c
index 4829c07..8ea7a80 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 
 /* Needed early for CONFIG_BSD etc. */
 
@@ -122,7 +123,7 @@ static int fcntl_op_getlk = -1;
 /*
  * Dups an fd and sets the flags
  */
-static int qemu_dup_flags(int fd, int flags)
+int qemu_dup_flags(int fd, int flags)
 {
     int ret;
     int serrno;
@@ -279,13 +280,27 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
 }
 #endif
 
+static int qemu_open_cloexec(const char *name, int flags, mode_t mode)
+{
+    int ret;
+#ifdef O_CLOEXEC
+    ret = open(name, flags | O_CLOEXEC, mode);
+#else
+    ret = open(name, flags, mode);
+    if (ret >= 0) {
+        qemu_set_cloexec(ret);
+    }
+#endif
+    return ret;
+}
+
 /*
  * Opens a file with FD_CLOEXEC set
  */
-int qemu_open(const char *name, int flags, ...)
+static int
+qemu_open_internal(const char *name, int flags, mode_t mode, Error **errp)
 {
     int ret;
-    int mode = 0;
 
 #ifndef _WIN32
     const char *fdset_id_str;
@@ -293,29 +308,19 @@ int qemu_open(const char *name, int flags, ...)
     /* Attempt dup of fd from fd set */
     if (strstart(name, "/dev/fdset/", &fdset_id_str)) {
         int64_t fdset_id;
-        int fd, dupfd;
+        int dupfd;
 
         fdset_id = qemu_parse_fdset(fdset_id_str);
         if (fdset_id == -1) {
+            error_setg(errp, "Could not parse fdset %s", name);
             errno = EINVAL;
             return -1;
         }
 
-        fd = monitor_fdset_get_fd(fdset_id, flags);
-        if (fd < 0) {
-            errno = -fd;
-            return -1;
-        }
-
-        dupfd = qemu_dup_flags(fd, flags);
+        dupfd = monitor_fdset_dup_fd_add(fdset_id, flags);
         if (dupfd == -1) {
-            return -1;
-        }
-
-        ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
-        if (ret == -1) {
-            close(dupfd);
-            errno = EINVAL;
+            error_setg_errno(errp, errno, "Could not dup FD for %s flags %x",
+                             name, flags);
             return -1;
         }
 
@@ -323,22 +328,61 @@ int qemu_open(const char *name, int flags, ...)
     }
 #endif
 
-    if (flags & O_CREAT) {
-        va_list ap;
+    ret = qemu_open_cloexec(name, flags, mode);
 
-        va_start(ap, flags);
-        mode = va_arg(ap, int);
-        va_end(ap);
+    if (ret == -1) {
+        const char *action = flags & O_CREAT ? "create" : "open";
+#ifdef O_DIRECT
+        /* Give more helpful error message for O_DIRECT */
+        if (errno == EINVAL && (flags & O_DIRECT)) {
+            ret = open(name, flags & ~O_DIRECT, mode);
+            if (ret != -1) {
+                close(ret);
+                error_setg(errp, "Could not %s '%s': "
+                           "filesystem does not support O_DIRECT",
+                           action, name);
+                errno = EINVAL; /* restore first open()'s errno */
+                return -1;
+            }
+        }
+#endif /* O_DIRECT */
+        error_setg_errno(errp, errno, "Could not %s '%s'",
+                         action, name);
     }
 
-#ifdef O_CLOEXEC
-    ret = open(name, flags | O_CLOEXEC, mode);
-#else
-    ret = open(name, flags, mode);
-    if (ret >= 0) {
-        qemu_set_cloexec(ret);
+    return ret;
+}
+
+
+int qemu_open(const char *name, int flags, Error **errp)
+{
+    assert(!(flags & O_CREAT));
+
+    return qemu_open_internal(name, flags, 0, errp);
+}
+
+
+int qemu_create(const char *name, int flags, mode_t mode, Error **errp)
+{
+    assert(!(flags & O_CREAT));
+
+    return qemu_open_internal(name, flags | O_CREAT, mode, errp);
+}
+
+
+int qemu_open_old(const char *name, int flags, ...)
+{
+    va_list ap;
+    mode_t mode = 0;
+    int ret;
+
+    va_start(ap, flags);
+    if (flags & O_CREAT) {
+        mode = va_arg(ap, int);
     }
-#endif
+    va_end(ap);
+
+    ret = qemu_open_internal(name, flags, mode, NULL);
 
 #ifdef O_DIRECT
     if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index ad8001a..f5f676f 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -125,7 +125,7 @@ bool qemu_write_pidfile(const char *path, Error **errp)
             .l_len = 0,
         };
 
-        fd = qemu_open(path, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
+        fd = qemu_open_old(path, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
         if (fd == -1) {
             error_setg_errno(errp, errno, "Cannot open pid file");
             return false;