basic: add quota-util.[ch] with some helpers for the Linux quotactl() API

src/basic/meson.build

@@ -169,6 +169,8 @@ basic_sources = files('''
         process-util.h
         procfs-util.c
         procfs-util.h
+        quota-util.c
+        quota-util.h
         random-util.c
         random-util.h
         ratelimit.c

src/basic/quota-util.c

@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <sys/quota.h>
+
+#include "alloc-util.h"
+#include "blockdev-util.h"
+#include "quota-util.h"
+#include "stat-util.h"
+
+int quotactl_devno(int cmd, dev_t devno, int id, void *addr) {
+        _cleanup_free_ char *devnode = NULL;
+        int r;
+
+        /* Like quotactl() but takes a dev_t instead of a path to a device node, and fixes caddr_t → void*,
+         * like we should, today */
+
+        r = device_path_make_major_minor(S_IFBLK, devno, &devnode);
+        if (r < 0)
+                return r;
+
+        if (quotactl(cmd, devnode, id, addr) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int quotactl_path(int cmd, const char *path, int id, void *addr) {
+        dev_t devno;
+        int r;
+
+        /* Like quotactl() but takes a path to some fs object, and changes the backing file system. I.e. the
+         * argument shouldn't be a block device but a regular file system object */
+
+        r = get_block_device(path, &devno);
+        if (r < 0)
+                return r;
+        if (devno == 0)
+                return -ENODEV;
+
+        return quotactl_devno(cmd, devno, id, addr);
+}

src/basic/quota-util.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+#include <inttypes.h>
+#include <sys/quota.h>
+#include <sys/types.h>
+
+/* Wrapper around the QCMD() macro of linux/quota.h that removes some undefined behaviour. A typical quota
+ * command such as QCMD(Q_GETQUOTA, USRQUOTA) cannot be resolved on platforms where "int" is 32bit, as it is
+ * larger than INT_MAX. Yikes, because that are basically all platforms Linux supports. Let's add a wrapper
+ * that explicitly takes its arguments as unsigned 32bit, and then converts the shift result explicitly to
+ * int, acknowledging the undefined behaviour of the kernel headers. This doesn't remove the undefined
+ * behaviour, but it stops ubsan from complaining about it. */
+static inline int QCMD_FIXED(uint32_t cmd, uint32_t type) {
+        return (int) QCMD(cmd, type);
+}
+
+int quotactl_devno(int cmd, dev_t devno, int id, void *addr);
+int quotactl_path(int cmd, const char *path, int id, void *addr);