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Subject[RFC PATCH 1/4] vfs: Create fs_context-aware mount_bdev() replacement
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Create a function, vfs_get_block_super(), that is fs_context-aware and a
replacement for mount_bdev(). It caches the block device pointer and file
open mode in the fs_context struct so that this information can be passed
into sget_fc()'s test and set functions.

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/fs_context.c | 2 +
fs/super.c | 106 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs_context.h | 6 ++
3 files changed, 114 insertions(+)

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 87e3546b9a52..ea027762c0b2 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -425,6 +425,8 @@ void put_fs_context(struct fs_context *fc)

if (fc->need_free && fc->ops && fc->ops->free)
fc->ops->free(fc);
+ if (fc->bdev)
+ blkdev_put(fc->bdev, fc->bdev_mode);

security_free_mnt_opts(&fc->security);
put_net(fc->net_ns);
diff --git a/fs/super.c b/fs/super.c
index f27ee08fb26f..85851adb0f19 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1211,6 +1211,112 @@ int vfs_get_super(struct fs_context *fc,
EXPORT_SYMBOL(vfs_get_super);

#ifdef CONFIG_BLOCK
+static int set_bdev_super_fc(struct super_block *s, struct fs_context *fc)
+{
+ s->s_bdev = fc->bdev;
+ s->s_dev = s->s_bdev->bd_dev;
+ s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
+ fc->bdev = NULL;
+ return 0;
+}
+
+static int test_bdev_super_fc(struct super_block *s, struct fs_context *fc)
+{
+ return s->s_bdev == fc->bdev;
+}
+
+/**
+ * vfs_get_block_super - Get a superblock based on a single block device
+ * @fc: The filesystem context holding the parameters
+ * @keying: How to distinguish superblocks
+ * @fill_super: Helper to initialise a new superblock
+ */
+int vfs_get_block_super(struct fs_context *fc,
+ int (*fill_super)(struct super_block *,
+ struct fs_context *))
+{
+ struct block_device *bdev;
+ struct super_block *s;
+ int error = 0;
+
+ fc->bdev_mode = FMODE_READ | FMODE_EXCL;
+ if (!(fc->sb_flags & SB_RDONLY))
+ fc->bdev_mode |= FMODE_WRITE;
+
+ if (!fc->source)
+ return invalf(fc, "No source specified");
+
+ bdev = blkdev_get_by_path(fc->source, fc->bdev_mode, fc->fs_type);
+ if (IS_ERR(bdev)) {
+ errorf(fc, "%s: Can't open blockdev", fc->source);
+ return PTR_ERR(bdev);
+ }
+
+ /* Once the superblock is inserted into the list by sget_fc(), s_umount
+ * will protect the lockfs code from trying to start a snapshot while
+ * we are mounting
+ */
+ mutex_lock(&bdev->bd_fsfreeze_mutex);
+ if (bdev->bd_fsfreeze_count > 0) {
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
+ error = -EBUSY;
+ goto error_bdev;
+ }
+
+ fc->bdev = bdev;
+ fc->sb_flags |= SB_NOSEC;
+ s = sget_fc(fc, test_bdev_super_fc, set_bdev_super_fc);
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ if (IS_ERR(s)) {
+ error = PTR_ERR(s);
+ goto error_bdev;
+ }
+
+ if (s->s_root) {
+ /* Don't summarily change the RO/RW state. */
+ if ((fc->sb_flags ^ s->s_flags) & SB_RDONLY) {
+ warnf(fc, "%pg: Can't mount, would change RO state", bdev);
+ error = -EBUSY;
+ goto error_sb;
+ }
+
+ /* s_umount nests inside bd_mutex during __invalidate_device().
+ * blkdev_put() acquires bd_mutex and can't be called under
+ * s_umount. Drop s_umount temporarily. This is safe as we're
+ * holding an active reference.
+ */
+ up_write(&s->s_umount);
+ blkdev_put(bdev, fc->bdev_mode);
+ down_write(&s->s_umount);
+ } else {
+ s->s_mode = fc->bdev_mode;
+ snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
+ sb_set_blocksize(s, block_size(bdev));
+ error = fill_super(s, fc);
+ if (error)
+ goto error_sb;
+
+ s->s_flags |= SB_ACTIVE;
+ bdev->bd_super = s;
+ }
+
+ BUG_ON(fc->root);
+ fc->root = dget(s->s_root);
+ return 0;
+
+error_sb:
+ deactivate_locked_super(s);
+error_bdev:
+ if (fc->bdev) {
+ blkdev_put(fc->bdev, fc->bdev_mode);
+ fc->bdev = NULL;
+ }
+ return error;
+}
+EXPORT_SYMBOL(vfs_get_block_super);
+
+
static int set_bdev_super(struct super_block *s, void *data)
{
s->s_bdev = data;
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index a779022d06f5..cb49b92f02af 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -76,6 +76,7 @@ struct fs_context {
const struct fs_context_operations *ops;
struct file_system_type *fs_type;
void *fs_private; /* The filesystem's context */
+ struct block_device *bdev; /* The backing blockdev (if applicable) */
struct dentry *root; /* The root and superblock */
struct user_namespace *user_ns; /* The user namespace for this mount */
struct net *net_ns; /* The network namespace for this mount */
@@ -84,6 +85,7 @@ struct fs_context {
const char *subtype; /* The subtype to set on the superblock */
void *security; /* Linux S&M options */
void *s_fs_info; /* Proposed s_fs_info */
+ fmode_t bdev_mode; /* File open mode for bdev */
unsigned int sb_flags; /* Proposed superblock flags (SB_*) */
unsigned int sb_flags_mask; /* Superblock flags that were changed */
unsigned int s_iflags; /* OR'd with sb->s_iflags */
@@ -141,6 +143,10 @@ extern int vfs_get_super(struct fs_context *fc,
int (*fill_super)(struct super_block *sb,
struct fs_context *fc));

+extern int vfs_get_block_super(struct fs_context *fc,
+ int (*fill_super)(struct super_block *sb,
+ struct fs_context *fc));
+
extern const struct file_operations fscontext_fops;

#ifdef CONFIG_PRINTK
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