feat: add support for dfs remount functionality

This patch introduces a remount feature for the DFS (Distributed File System), allowing
for the modification of mount parameters without unmounting the filesystem. This was
necessary to enhance flexibility and improve system management by enabling dynamic
adjustments to filesystem settings.

Changes:
- Defined new constants for remount flags in `dfs_fs.h`.
- Added the `dfs_remount()` function in `dfs_fs.c` to handle remount operations.
- Introduced a check for unsupported flags and handle error conditions such as invalid paths
  or non-directory targets.
- Updated the `dfs_mnt` structure in `dfs_mnt.h` to include a read-only flag (`MNT_RDONLY`).
- The `dfs_remount()` function allows changing the read-only status of a mounted filesystem.

The remount functionality helps modify certain mount flags (like `MS_RDONLY`) without
requiring an unmount, providing more control over mounted filesystems in the system.

Signed-off-by: Shell <[email protected]>

Author: polarvid

components/dfs/dfs_v2/include/dfs_fs.h

@@ -20,6 +20,38 @@ extern "C"
 {
 #endif
 
+#define MS_RDONLY      1
+#define MS_NOSUID      2
+#define MS_NODEV       4
+#define MS_NOEXEC      8
+#define MS_SYNCHRONOUS 16
+#define MS_REMOUNT     32
+#define MS_MANDLOCK    64
+#define MS_DIRSYNC     128
+#define MS_NOATIME     1024
+#define MS_NODIRATIME  2048
+#define MS_BIND        4096
+#define MS_MOVE        8192
+#define MS_REC         16384
+#define MS_SILENT      32768
+#define MS_POSIXACL    (1<<16)
+#define MS_UNBINDABLE  (1<<17)
+#define MS_PRIVATE     (1<<18)
+#define MS_SLAVE       (1<<19)
+#define MS_SHARED      (1<<20)
+#define MS_RELATIME    (1<<21)
+#define MS_KERNMOUNT   (1<<22)
+#define MS_I_VERSION   (1<<23)
+#define MS_STRICTATIME (1<<24)
+#define MS_LAZYTIME    (1<<25)
+#define MS_NOREMOTELOCK (1<<27)
+#define MS_NOSEC       (1<<28)
+#define MS_BORN        (1<<29)
+#define MS_ACTIVE      (1<<30)
+#define MS_NOUSER      (1U<<31)
+
+#define MS_RMT_MASK (MS_RDONLY|MS_SYNCHRONOUS|MS_MANDLOCK|MS_I_VERSION|MS_LAZYTIME)
+
 /* file system partition table */
 struct dfs_partition
 {
@@ -87,6 +119,7 @@ int dfs_unregister(struct dfs_filesystem_type *fs);
 int dfs_register(struct dfs_filesystem_type *fs);
 const char *dfs_filesystem_get_mounted_path(struct rt_device *device);
 
+int dfs_remount(const char *path, rt_ubase_t flags, void *data);
 int dfs_mount(const char *device_name,
             const char *path,
             const char *filesystemtype,

components/dfs/dfs_v2/include/dfs_mnt.h

@@ -39,6 +39,7 @@ struct dfs_mnt
 #define MNT_IS_UMOUNT  0x8          /* the mnt is unmount */
 #define MNT_IS_LOCKED  0x10         /* the mnt is locked */
 #define MNT_FORCE      0x20         /* the mnt force unmount */
+#define MNT_RDONLY     0x80         /* the mnt is read only */
 
     rt_atomic_t ref_count;          /* reference count */
 

components/dfs/dfs_v2/src/dfs_fs.c

@@ -95,6 +95,55 @@ int dfs_unregister(struct dfs_filesystem_type *fs)
     return ret;
 }
 
+#define REMNT_UNSUPP_FLAGS (~(MS_REMOUNT | MS_RMT_MASK))
+int dfs_remount(const char *path, rt_ubase_t flags, void *data)
+{
+    int rc = 0;
+    char *fullpath = RT_NULL;
+    struct dfs_mnt *mnt = RT_NULL;
+
+    if (flags & REMNT_UNSUPP_FLAGS)
+    {
+        return -EINVAL;
+    }
+
+    fullpath = dfs_normalize_path(RT_NULL, path);
+    if (!fullpath)
+    {
+        rc = -ENOENT;
+    }
+    else
+    {
+        DLOG(msg, "dfs", "mnt", DLOG_MSG, "mnt = dfs_mnt_lookup(%s)", fullpath);
+        mnt = dfs_mnt_lookup(fullpath);
+        if (mnt)
+        {
+            dfs_lock();
+            if (flags & MS_RDONLY)
+            {
+                mnt->flags |= MNT_RDONLY;
+            }
+            dfs_unlock();
+        }
+        else
+        {
+            struct stat buf = {0};
+            if (dfs_file_stat(fullpath, &buf) == 0 && S_ISBLK(buf.st_mode))
+            {
+                /* path was not already mounted on target */
+                rc = -EINVAL;
+            }
+            else
+            {
+                /* path is not a directory */
+                rc = -ENOTDIR;
+            }
+        }
+    }
+
+    return rc;
+}
+
 /*
  *    parent(mount path)
  *    mnt_parent <- - - - - - -  +