BlobFS | Fuchsia

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2022-05-12 06:30:09

BlobFS is a content-addressable filesystem optimized for write-once, read-often files, such as binaries and libraries. On Fuchsia, BlobFS is the storage system used for all software packages.

These properties of blobs make BlobfS a key component of Fuchsia's security posture, ensuring that software packages' contents can be verified before they are executed.

BlobFS stores each blob in a linked list of non-adjacent extents (a contiguous range of data blocks). Each blob has an associated Inode, which describes where the block's data starts on disk and other metadata about the blob.

The superblock is the first block in a BlobFS-formatted partition. It describes the location and size of the other chunks of the filesystem, as well as other filesystem-level metadata.

When a BlobFS-formatted filesystem is mounted, this block is mapped into memory and parsed to determine where the rest of the filesystem lives. The block is modified whenever a new blob is created, and (for FVM-managed BlobFS instances) whenever the size of the BlobFS filesystem shrinks or grows.