Re: [PATCH V11 4/9] famfs_fuse: Create files with famfs fmaps

[Miklos Szeredi]

On Mon, 20 Jul 2026 at 05:46, John Groves <john@xxxxxxxxxxxxxx> wrote:

> +/* Famfs fmap message components */
> +
> +#define FAMFS_FMAP_VERSION 1

Please don't use separate versioning for extents.  It doesn't help
with feature negotiation, so let's just use the INIT feature flags for
this purpose.

> +
> +#define FAMFS_FMAP_MAX 32768 /* Largest supported fmap message */

Not sure if it makes sense declaring this on the user API.

> +
> +enum fuse_famfs_file_type {
> +       FUSE_FAMFS_FILE_REG,
> +       FUSE_FAMFS_FILE_SUPERBLOCK,
> +       FUSE_FAMFS_FILE_LOG,
> +};

Unused, apparently.

> +
> +enum famfs_ext_type {
> +       FUSE_FAMFS_EXT_SIMPLE = 0,
> +};

An enum with a single value is not useful.

> +
> +struct fuse_famfs_simple_ext {

struct fuse_extent {

> +       uint32_t se_devindex;

uint64_t backing_id.

> +       uint32_t reserved;
> +       uint64_t se_offset;
> +       uint64_t se_len;

Please  drop the "se_" prefix.

Please add more spare space here (e.g. uint64_t space[3]).

> +};

> +
> +struct fuse_famfs_fmap_header {

struct fuse_extents_header {

> +       uint8_t file_type; /* enum fuse_famfs_file_type */

Unused

> +       uint8_t reserved;
> +       uint16_t fmap_version;

Don't use, plese.

> +       uint32_t ext_type; /* enum famfs_ext_type */

Unused.

> +       uint32_t nextents;

Okay.

> +       uint32_t fmap_size; /* Inclusive of this header */

That's the same as outh.len.

> +       uint64_t file_size;

Same as i_size

Thanks,
Miklos