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Add 'zero-copy' in libiscsi for reads.

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It is not real zero-copy since the data is still copied in the kernel,
but it avoids copying the data inside libiscsi as well as in the callback.

For SCSI tasks that will return data from the target, the application can now
specify application buffers for libiscsi to read the data directly into.
This is done by calling scsi_task_add_data_in_buffer(task, ...

These buffers need not be linear, you can specify different areas to read into
by calling this function several times.

See examples/iscsiclient.c for an example.
This commit is contained in:
Ronnie Sahlberg
2011-04-20 05:42:36 +10:00
parent acc2871ab0
commit 3a39201543
10 changed files with 146 additions and 19 deletions
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25
lib/socket.c
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@@ -267,13 +267,7 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
data_size = iscsi_get_pdu_data_size(&in->hdr[0]);
if (data_size != 0) {
if (in->data == NULL) {
in->data = malloc(data_size);
if (in->data == NULL) {
iscsi_set_error(iscsi, "Out-of-memory: failed to malloc iscsi_in_pdu->data(%d)", (int)data_size);
return -1;
}
}
unsigned char *buf = NULL;
/* No more data right now */
if (socket_count == 0) {
@@ -283,7 +277,22 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
if (count > socket_count) {
count = socket_count;
}
count = read(iscsi->fd, &in->data[in->data_pos], count);
/* first try to see if we already have a user buffer */
buf = iscsi_get_user_in_buffer(iscsi, in, in->data_pos, &count);
/* if not, allocate one */
if (buf == NULL) {
if (in->data == NULL) {
in->data = malloc(data_size);
if (in->data == NULL) {
iscsi_set_error(iscsi, "Out-of-memory: failed to malloc iscsi_in_pdu->data(%d)", (int)data_size);
return -1;
}
}
buf = &in->data[in->data_pos];
}
count = read(iscsi->fd, buf, count);
if (count < 0) {
if (errno == EINTR) {
return 0;