man: Fix uninitialized err_entry

[rd-cea]

fi_cq_readerr was previously called on uninitialized .err_data and .err_data_size in a code snippet from fi_setup.7.md:

/* Sample error handling */
struct fi_cq_msg_entry entry;
struct fi_cq_err_entry err_entry;
int ret;

ret = fi_cq_read(cq, &entry, 1);
if (ret == -FI_EAVAIL)
    ret = fi_cq_readerr(cq, &err_entry, 0);

According to fi_cq.3.md however, both .err_data and .err_data_size must be initialized prior to any call to fi_cq_readerr.

err_data : The err_data field is used to return provider specific information, if available, about the error. On input, err_data should reference a data buffer of size err_data_size. On output, the provider will fill in this buffer with any provider specific data which may help identify the cause of the error. The contents of the err_data field and its meaning is provider specific. It is intended to be used as a debugging aid. See fi_cq_strerror for additional details on converting this error data into a human readable string. See the compatibility note below on how this field is used for older libfabric releases.

err_data_size : On input, err_data_size indicates the size of the err_data buffer in bytes. On output, err_data_size will be set to the number of bytes copied to the err_data buffer. The err_data information is typically used with fi_cq_strerror to provide details about the type of error that occurred.

By looking at the source code and at Valgrind errors in my application based on this code snippet, input .err_data and .err_data_size are used in ofi_cq_readerr, and must indeed be initialized.

libfabric/prov/util/src/util_cq.c

Line 287 in 8b40238

size_t err_data_size = buf->err_data_size;

[j-xiong]

Thanks!