DAOS-15847 object: restore iov_len for fetch on dup-only (no-merge) SGLs (#18413)

In obj_dup_sgls_free(), when ctx->alloc_bitmaps[i] == NULL, the function skips
the entire SGL with `continue`:
    if (!ctx->alloc_bitmaps || !ctx->alloc_bitmaps[i])
        continue;

This case arises when a SGL was duplicated only to strip iov_buf_len==0 entries
(skip_sgl_iov returned true) but no IOVs were merged into allocated buffers.
During construction (second pass of obj_sgls_dup), non-merged IOVs are copied as:
    *iov_dup = *iov;
So iov_dup->iov_buf == iov->iov_buf (same pointer).  The lower layer writes
fetch data into iov_dup->iov_buf and updates iov_dup->iov_len to reflect actual
bytes read.
Because obj_dup_sgls_free skips such SGLs, iov->iov_len in the *original* SGL
is never updated.  After api_args->sgls is restored to orr_usgls, the caller sees
stale pre-fetch iov_len values even though the data is in the correct buffers.

Signed-off-by: Xuezhao Liu <xuezhao.liu@hpe.com>

Author: liuxuezhao

src/object/cli_obj.c

@@ -4943,8 +4943,26 @@ obj_dup_sgls_free(struct obj_auxi_args *obj_auxi)
 			uint32_t     dup_data_len = 0;
 			char        *dup_buf;
 
-			if (!ctx->alloc_bitmaps || !ctx->alloc_bitmaps[i])
+			if (!ctx->alloc_bitmaps || !ctx->alloc_bitmaps[i]) {
+				/* SGL was duplicated (e.g. to strip zero-buf-len
+				 * entries) but has no merged/allocated buffers.
+				 * Dup IOVs share the same iov_buf pointers as the
+				 * originals, so fetch data is already in place.
+				 * Copy iov_len back so the caller sees actual bytes
+				 * read, and update sg_nr_out accordingly.
+				 */
+				uint32_t dup_idx = 0;
+
+				for (j = 0; j < sg_orig->sg_nr && dup_idx < sg_dup->sg_nr_out;
+				     j++) {
+					iov = &sg_orig->sg_iovs[j];
+					if (skip_sgl_iov(false, iov))
+						continue;
+					iov->iov_len = sg_dup->sg_iovs[dup_idx++].iov_len;
+				}
+				sg_orig->sg_nr_out = j;
 				continue;
+			}
 
 			D_ASSERT(ctx->merged_bitmaps[i] != NULL);
 			for (j = 0; j < sg_orig->sg_nr && dup_sg_idx < sg_dup->sg_nr_out; j++) {
@@ -4989,7 +5007,6 @@ obj_dup_sgls_free(struct obj_auxi_args *obj_auxi)
 	D_FREE(ctx);
 	obj_auxi->rw_args.merge_ctx = NULL;
 	api_args                    = dc_task_get_args(obj_auxi->obj_task);
-	api_args                    = dc_task_get_args(obj_auxi->obj_task);
 	api_args->sgls              = obj_auxi->reasb_req.orr_usgls;
 }