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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
Download Patch File Download Diff File Expand all files Collapse all files

39
lib/scsi-command.c
View File

@@ -435,12 +435,15 @@ iscsi_process_scsi_data_in(struct iscsi_context *iscsi, struct iscsi_pdu *pdu,
}
dsl = ntohl(*(uint32_t *)&in->hdr[4])&0x00ffffff;
if (iscsi_add_data(iscsi, &pdu->indata,
in->data, dsl, 0)
!= 0) {
iscsi_set_error(iscsi, "Out-of-memory: failed to add data "
/* Dont add to reassembly buffer if we already have a user buffer */
if (scsi_task_get_data_in_buffer(task, 0, NULL) == NULL) {
if (iscsi_add_data(iscsi, &pdu->indata,
in->data, dsl, 0)
!= 0) {
iscsi_set_error(iscsi, "Out-of-memory: failed to add data "
"to pdu in buffer.");
return -1;
return -1;
}
}
@@ -733,3 +736,29 @@ iscsi_synchronizecache10_task(struct iscsi_context *iscsi, int lun, int lba,
return task;
}
unsigned char *
iscsi_get_user_in_buffer(struct iscsi_context *iscsi, struct iscsi_in_pdu *in, uint32_t pos, ssize_t *count)
{
struct iscsi_pdu *pdu;
uint32_t len, offset;
uint32_t itt;
if ((in->hdr[0] & 0x3f) != ISCSI_PDU_DATA_IN) {
return NULL;
}
len = ntohl(*(uint32_t *)&in->hdr[4])&0x00ffffff;
offset = ntohl(*(uint32_t *)&in->hdr[40]);
itt = ntohl(*(uint32_t *)&in->hdr[16]);
for (pdu = iscsi->waitpdu; pdu; pdu = pdu->next) {
if (pdu->itt == itt) {
break;
}
}
if (pdu == NULL) {
return NULL;
}
return scsi_task_get_data_in_buffer(pdu->scsi_cbdata->task, offset + pos, count);
}