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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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21
examples/iscsiclient.c
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@@ -13,7 +13,7 @@
*/
/* This is the host/port we connect to.*/
#define TARGET "127.0.0.1:3260"
#define TARGET "10.1.1.27:3260"
#include <stdio.h>
#include <stdlib.h>
@@ -33,6 +33,8 @@ struct client_state {
int block_size;
};
unsigned char small_buffer[512];
void tm_at_cb(struct iscsi_context *iscsi _U_, int status _U_, void *command_data _U_, void *private_data)
{
struct client_state *clnt = (struct client_state *)private_data;
@@ -105,8 +107,8 @@ void read10_cb(struct iscsi_context *iscsi, int status, void *command_data, void
}
printf("READ10 successful. Block content:\n");
for (i=0;i<task->datain.size;i++) {
printf("%02x ", task->datain.data[i]);
for (i=0;i<512;i++) {
printf("%02x ", small_buffer[i]);
if (i%16==15)
printf("\n");
if (i==69)
@@ -152,12 +154,19 @@ void read6_cb(struct iscsi_context *iscsi, int status, void *command_data, void
}
printf("...\n");
if (iscsi_read10_task(iscsi, clnt->lun, 0, clnt->block_size, clnt->block_size, read10_cb, private_data) == NULL) {
scsi_free_scsi_task(task);
if ((task = iscsi_read10_task(iscsi, clnt->lun, 0, clnt->block_size, clnt->block_size, read10_cb, private_data)) == NULL) {
printf("failed to send read10 command\n");
scsi_free_scsi_task(task);
exit(10);
}
scsi_free_scsi_task(task);
/* provide a buffer from the application to read into instead
* of copying and linearizing the data. This saves two copies
* of the data. One in libiscsi and one in the application
* callback.
*/
scsi_task_add_data_in_buffer(task, 128, &small_buffer[0]);
scsi_task_add_data_in_buffer(task, 512-128, &small_buffer[128]);
}
void readcapacity10_cb(struct iscsi_context *iscsi, int status, void *command_data, void *private_data)