Fix directory operations to comply with ISO 11783-13:2021 (sections
C.3.4.2 and C.3.5.2), which specifies that 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.
The previous implementation treated directories strictly as files,
using byte-based offsets and counts. This resulted in incorrect seeking
behavior and protocol violations when listing directories.
Align the implementation with the standard by:
1. Server side:
- Introduce isobusfs_srv_dir_entry_visible() to consistently
filter out invalid (unreadable, hidden, oversized) entries. This
ensures that entry indices remain stable.
- Implement isobusfs_srv_dir_skip_entries() to advance the
directory stream by logical visible entries rather than bytes.
- Update the Read File handler to interpret count as the
maximum number of entries and return the number of entries read
in the response header.
- Update the Seek File handler to seek by entry index.
2. Client side:
- Calculate the request count based on the number of minimal-size
entries that fit into the maximum data length.
- Interpret 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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