According to ISO 11783-13:2021 (sections C.3.4.2 and C.3.5.2), directory
operations differ significantly from standard file operations:
- The `Count` parameter in a "Read File" request represents the number of
directory entries to read, not the number of bytes.
- The `Offset` parameter in a "Seek File" request represents the logical
entry index, not a byte offset.
Previously, the implementation treated directories strictly as files,
using byte-based offsets and counts. This resulted in incorrect seeking
behavior and protocol violations when listing directories.
This patch aligns the implementation with the standard by:
1. Server side:
- Introducing `isobusfs_srv_dir_entry_visible()` to consistently
filter out invalid (unreadable, hidden, oversized) entries. This
ensures that entry indices remain stable.
- Implementing `isobusfs_srv_dir_skip_entries()` to advance the
directory stream by logical visible entries rather than bytes.
- Updating the "Read File" handler to interpret `count` as the
maximum number of entries and return the number of entries read
in the response header.
- Updating the "Seek File" handler to seek by entry index.
2. Client side:
- Calculating the request count based on the number of minimal-size
entries that fit into the maximum data length.
- Interpreting the response `count` as the number of entries received
rather than the byte length of the payload.
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
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