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ecm fix fix partial extend #245

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Merged
PerditionC merged 2 commits into from
Apr 22, 2026
Merged

ecm fix fix partial extend #245

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f2b939c
fatfs.c: fix earlier fix, update dir_size in map_cluster loop
ecm-pushbx Apr 22, 2026
c63f9f4
fatfs.c: comment unexpected alloc of cluster past needed if CX=0
ecm-pushbx Apr 22, 2026
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14 changes: 13 additions & 1 deletion kernel/fatfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1029,7 +1029,7 @@ COUNT map_cluster(REG f_node_ptr fnp, COUNT mode)
fnp->f_cluster = cluster;
fnp->f_cluster_offset++;
fnp->f_dir.dir_size =
((ULONG)fnp->f_cluster
(((ULONG)fnp->f_cluster_offset + 1)
* (ULONG)fnp->f_dpb->dpb_secsize)
<<
fnp->f_dpb->dpb_shftcnt;
Expand Down Expand Up @@ -1218,9 +1218,21 @@ long rwblock(COUNT fd, VOID FAR * buffer, UCOUNT count, int mode)

if (dos_extend(fnp) != SUCCESS)
{
/* ecm: control flow may end up here if CX = 0000h and
the extending failed to allocate a cluster
behind the last needed. in this case, our
return here of 0 happens to be correct and
indicates the extension succeeded. */
fnode_to_sft(fnp);
return 0;
}
/* ecm: if CX = 0000h and seek was on a cluster boundary > size,
the dos_extend call will have allocated one cluster
too many. this is truncated later without problems.
but does this aid fragmentation maybe ?
if CX > 0000h then we want to write to the cluster
anyway, so extending to the cluster that starts at
the boundary is desired. */
}

/* Test that we are really about to do a data transfer. If the */
Expand Down