erofs: add fscache mode check helper

Until then erofs is exactly blockdev based filesystem.

A new fscache-based mode is going to be introduced for erofs to support
scenarios where on-demand read semantics is needed, e.g. container
image distribution. In this case, erofs could be mounted from data blobs
through fscache.

Add a helper checking which mode erofs works in, and twist the code in
preparation for the upcoming fscache mode.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220425122143.56815-11-jefflexu@linux.alibaba.com
Acked-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index c83bd3965cb50e050ca1bc0e7f524d04da357074..52911eaf36f6a34b8cc3a82ba6f1cbee9399b9f4 100644 (file)
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -161,6 +161,11 @@ struct erofs_sb_info {
 #define set_opt(opt, option)   ((opt)->mount_opt |= EROFS_MOUNT_##option)
 #define test_opt(opt, option)  ((opt)->mount_opt & EROFS_MOUNT_##option)
 
+static inline bool erofs_is_fscache_mode(struct super_block *sb)
+{
+       return IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && !sb->s_bdev;
+}
+
 enum {
        EROFS_ZIP_CACHE_DISABLED,
        EROFS_ZIP_CACHE_READAHEAD,

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index a326445af7d0c581bf4a2930f341b9ceeda3fdd2..46ca7917cb2a4e089c4db1ab64c0fb8bb7e88f43 100644 (file)
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -260,15 +260,19 @@ static int erofs_init_devices(struct super_block *sb,
                }
                dis = ptr + erofs_blkoff(pos);
 
-               bdev = blkdev_get_by_path(dif->path,
-                                         FMODE_READ | FMODE_EXCL,
-                                         sb->s_type);
-               if (IS_ERR(bdev)) {
-                       err = PTR_ERR(bdev);
-                       break;
+               if (!erofs_is_fscache_mode(sb)) {
+                       bdev = blkdev_get_by_path(dif->path,
+                                                 FMODE_READ | FMODE_EXCL,
+                                                 sb->s_type);
+                       if (IS_ERR(bdev)) {
+                               err = PTR_ERR(bdev);
+                               break;
+                       }
+                       dif->bdev = bdev;
+                       dif->dax_dev = fs_dax_get_by_bdev(bdev,
+                                                         &dif->dax_part_off);
                }
-               dif->bdev = bdev;
-               dif->dax_dev = fs_dax_get_by_bdev(bdev, &dif->dax_part_off);
+
                dif->blocks = le32_to_cpu(dis->blocks);
                dif->mapped_blkaddr = le32_to_cpu(dis->mapped_blkaddr);
                sbi->total_blocks += dif->blocks;
@@ -625,21 +629,28 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 
        sb->s_magic = EROFS_SUPER_MAGIC;
 
-       if (!sb_set_blocksize(sb, EROFS_BLKSIZ)) {
-               erofs_err(sb, "failed to set erofs blksize");
-               return -EINVAL;
-       }
-
        sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
        if (!sbi)
                return -ENOMEM;
 
        sb->s_fs_info = sbi;
        sbi->opt = ctx->opt;
-       sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev, &sbi->dax_part_off);
        sbi->devs = ctx->devs;
        ctx->devs = NULL;
 
+       if (erofs_is_fscache_mode(sb)) {
+               sb->s_blocksize = EROFS_BLKSIZ;
+               sb->s_blocksize_bits = LOG_BLOCK_SIZE;
+       } else {
+               if (!sb_set_blocksize(sb, EROFS_BLKSIZ)) {
+                       erofs_err(sb, "failed to set erofs blksize");
+                       return -EINVAL;
+               }
+
+               sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev,
+                                                 &sbi->dax_part_off);
+       }
+
        err = erofs_read_superblock(sb);
        if (err)
                return err;
@@ -897,7 +908,10 @@ static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
        struct super_block *sb = dentry->d_sb;
        struct erofs_sb_info *sbi = EROFS_SB(sb);
-       u64 id = huge_encode_dev(sb->s_bdev->bd_dev);
+       u64 id = 0;
+
+       if (!erofs_is_fscache_mode(sb))
+               id = huge_encode_dev(sb->s_bdev->bd_dev);
 
        buf->f_type = sb->s_magic;
        buf->f_bsize = EROFS_BLKSIZ;