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Fix intermittent VCI signature failure in cart coherency MAM #623

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Fix intermittent VCI signature failure in cart coherency MAM #623

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11 changes: 11 additions & 0 deletions src/libltfs/tape.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1772,6 +1772,17 @@ int tape_set_cart_coherency(struct device_data *dev, const tape_partition_t part
CHECK_ARG_NULL(dev, -LTFS_NULL_ARG);
CHECK_ARG_NULL(dev->backend, -LTFS_NULL_ARG);

/* Zero the whole buffer so any byte not written explicitly below is
* deterministic. In particular byte 36 (the byte following the 4-char
* "LTFS" signature) is never assigned: arch_strncpy() copies exactly 4
* bytes and, since the count equals strlen("LTFS"), strncpy() writes no
* terminating NUL on POSIX. Without this memset that byte would carry
* uninitialized stack data onto the medium, and tape_get_cart_coherency()
* compares the signature with sizeof("LTFS") == 5 bytes, so a non-zero
* byte 36 makes the read-back fail (LTFS12062W) and forces a full
* consistency check on the next mount. */
memset(coh_data, 0, sizeof(coh_data));

ltfs_u16tobe(coh_data, TC_MAM_PAGE_COHERENCY);
coh_data[2] = 0;
ltfs_u16tobe(coh_data + 3, TC_MAM_PAGE_COHERENCY_SIZE);
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