mtd: Provide fs_context-aware mount_mtd() replacement

Provide a function, get_tree_mtd(), to replace mount_mtd(), using an
fs_context struct to hold the parameters.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: David Woodhouse <dwmw2@infradead.org>
cc: Brian Norris <computersforpeace@gmail.com>
cc: Boris Brezillon <bbrezillon@kernel.org>
cc: Marek Vasut <marek.vasut@gmail.com>
cc: Richard Weinberger <richard@nod.at>
cc: linux-mtd@lists.infradead.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 181 insertions, 2 deletions

diff --git a/drivers/mtd/mtdcore.h b/drivers/mtd/mtdcore.h
index b31c868019ad..b5eefeabf310 100644
--- a/drivers/mtd/mtdcore.h
+++ b/drivers/mtd/mtdcore.h
@@ -5,6 +5,7 @@
  */
 
 extern struct mutex mtd_table_mutex;
+extern struct backing_dev_info *mtd_bdi;
 
 struct mtd_info *__mtd_next_device(int i);
 int __must_check add_mtd_device(struct mtd_info *mtd);
diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
index 4f042a3653ce..3f9a3b7b12c5 100644
--- a/drivers/mtd/mtdsuper.c
+++ b/drivers/mtd/mtdsuper.c
@@ -15,6 +15,183 @@
 #include <linux/slab.h>
 #include <linux/major.h>
 #include <linux/backing-dev.h>
+#include <linux/fs_context.h>
+#include "mtdcore.h"
+
+/*
+ * compare superblocks to see if they're equivalent
+ * - they are if the underlying MTD device is the same
+ */
+static int mtd_test_super(struct super_block *sb, struct fs_context *fc)
+{
+        struct mtd_info *mtd = fc->sget_key;
+
+        if (sb->s_mtd == fc->sget_key) {
+                pr_debug("MTDSB: Match on device %d (\"%s\")\n",
+                         mtd->index, mtd->name);
+                return 1;
+        }
+
+        pr_debug("MTDSB: No match, device %d (\"%s\"), device %d (\"%s\")\n",
+                 sb->s_mtd->index, sb->s_mtd->name, mtd->index, mtd->name);
+        return 0;
+}
+
+/*
+ * mark the superblock by the MTD device it is using
+ * - set the device number to be the correct MTD block device for pesuperstence
+ *   of NFS exports
+ */
+static int mtd_set_super(struct super_block *sb, struct fs_context *fc)
+{
+        sb->s_mtd = fc->sget_key;
+        sb->s_dev = MKDEV(MTD_BLOCK_MAJOR, sb->s_mtd->index);
+        sb->s_bdi = bdi_get(mtd_bdi);
+        return 0;
+}
+
+/*
+ * get a superblock on an MTD-backed filesystem
+ */
+static int mtd_get_sb(struct fs_context *fc,
+                      struct mtd_info *mtd,
+                      int (*fill_super)(struct super_block *,
+                                        struct fs_context *))
+{
+        struct super_block *sb;
+        int ret;
+
+        fc->sget_key = mtd;
+        sb = sget_fc(fc, mtd_test_super, mtd_set_super);
+        if (IS_ERR(sb))
+                return PTR_ERR(sb);
+
+        if (sb->s_root) {
+                /* new mountpoint for an already mounted superblock */
+                pr_debug("MTDSB: Device %d (\"%s\") is already mounted\n",
+                         mtd->index, mtd->name);
+                put_mtd_device(mtd);
+        } else {
+                /* fresh new superblock */
+                pr_debug("MTDSB: New superblock for device %d (\"%s\")\n",
+                         mtd->index, mtd->name);
+
+                ret = fill_super(sb, fc);
+                if (ret < 0)
+                        goto error_sb;
+
+                sb->s_flags |= SB_ACTIVE;
+        }
+
+        BUG_ON(fc->root);
+        fc->root = dget(sb->s_root);
+        return 0;
+
+error_sb:
+        deactivate_locked_super(sb);
+        return ret;
+}
+
+/*
+ * get a superblock on an MTD-backed filesystem by MTD device number
+ */
+static int mtd_get_sb_by_nr(struct fs_context *fc, int mtdnr,
+                            int (*fill_super)(struct super_block *,
+                                              struct fs_context *))
+{
+        struct mtd_info *mtd;
+
+        mtd = get_mtd_device(NULL, mtdnr);
+        if (IS_ERR(mtd)) {
+                errorf(fc, "MTDSB: Device #%u doesn't appear to exist\n", mtdnr);
+                return PTR_ERR(mtd);
+        }
+
+        return mtd_get_sb(fc, mtd, fill_super);
+}
+
+/**
+ * get_tree_mtd - Get a superblock based on a single MTD device
+ * @fc: The filesystem context holding the parameters
+ * @fill_super: Helper to initialise a new superblock
+ */
+int get_tree_mtd(struct fs_context *fc,
+              int (*fill_super)(struct super_block *sb,
+                                struct fs_context *fc))
+{
+#ifdef CONFIG_BLOCK
+        struct block_device *bdev;
+        int ret, major;
+#endif
+        int mtdnr;
+
+        if (!fc->source)
+                return invalf(fc, "No source specified");
+
+        pr_debug("MTDSB: dev_name \"%s\"\n", fc->source);
+
+        /* the preferred way of mounting in future; especially when
+         * CONFIG_BLOCK=n - we specify the underlying MTD device by number or
+         * by name, so that we don't require block device support to be present
+         * in the kernel.
+         */
+        if (fc->source[0] == 'm' &&
+            fc->source[1] == 't' &&
+            fc->source[2] == 'd') {
+                if (fc->source[3] == ':') {
+                        struct mtd_info *mtd;
+
+                        /* mount by MTD device name */
+                        pr_debug("MTDSB: mtd:%%s, name \"%s\"\n",
+                                 fc->source + 4);
+
+                        mtd = get_mtd_device_nm(fc->source + 4);
+                        if (!IS_ERR(mtd))
+                                return mtd_get_sb(fc, mtd, fill_super);
+
+                        errorf(fc, "MTD: MTD device with name \"%s\" not found",
+                               fc->source + 4);
+
+                } else if (isdigit(fc->source[3])) {
+                        /* mount by MTD device number name */
+                        char *endptr;
+
+                        mtdnr = simple_strtoul(fc->source + 3, &endptr, 0);
+                        if (!*endptr) {
+                                /* It was a valid number */
+                                pr_debug("MTDSB: mtd%%d, mtdnr %d\n", mtdnr);
+                                return mtd_get_sb_by_nr(fc, mtdnr, fill_super);
+                        }
+                }
+        }
+
+#ifdef CONFIG_BLOCK
+        /* try the old way - the hack where we allowed users to mount
+         * /dev/mtdblock$(n) but didn't actually _use_ the blockdev
+         */
+        bdev = lookup_bdev(fc->source);
+        if (IS_ERR(bdev)) {
+                ret = PTR_ERR(bdev);
+                errorf(fc, "MTD: Couldn't look up '%s': %d", fc->source, ret);
+                return ret;
+        }
+        pr_debug("MTDSB: lookup_bdev() returned 0\n");
+
+        major = MAJOR(bdev->bd_dev);
+        mtdnr = MINOR(bdev->bd_dev);
+        bdput(bdev);
+
+        if (major == MTD_BLOCK_MAJOR)
+                return mtd_get_sb_by_nr(fc, mtdnr, fill_super);
+
+#endif /* CONFIG_BLOCK */
+
+        if (!(fc->sb_flags & SB_SILENT))
+                errorf(fc, "MTD: Attempt to mount non-MTD device \"%s\"",
+                       fc->source);
+        return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(get_tree_mtd);
 
 /*
  * compare superblocks to see if they're equivalent
@@ -35,8 +212,6 @@ static int get_sb_mtd_compare(struct super_block *sb, void *_mtd)
         return 0;
 }
 
-extern struct backing_dev_info *mtd_bdi;
-
 /*
  * mark the superblock by the MTD device it is using
  * - set the device number to be the correct MTD block device for pesuperstence
diff --git a/include/linux/mtd/super.h b/include/linux/mtd/super.h
index 056c9932c723..42db3f8e8136 100644
--- a/include/linux/mtd/super.h
+++ b/include/linux/mtd/super.h
@@ -14,6 +14,9 @@
 #include <linux/fs.h>
 #include <linux/mount.h>
 
+extern int get_tree_mtd(struct fs_context *fc,
+                     int (*fill_super)(struct super_block *sb,
+                                       struct fs_context *fc));
 extern struct dentry *mount_mtd(struct file_system_type *fs_type, int flags,
                       const char *dev_name, void *data,
                       int (*fill_super)(struct super_block *, void *, int));