Hi,
The utility I mentioned is just a small program that I wrote to learn
more about the problem.
It is a very simple read16 with options for mmap and dxferp as null or other.
Here is the source code:
== cut here ==
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <errno.h>
#include <getopt.h>
#include <unistd.h>
#include <fcntl.h>
#include <scsi/sg.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
void* prepare_addr_fd(const char* devname, size_t block_size, int* fd,
int fmmap)
{
void* addr = NULL;
int sg_fd;
if ((sg_fd = open(devname, O_RDWR)) < 0) {
fprintf(stderr, "failed to open %s: %s\n", devname, strerror(errno));
exit(1);
}
if (fmmap) {
addr = mmap(NULL, block_size, (PROT_READ | PROT_WRITE),
MAP_SHARED, sg_fd, 0);
if (addr == MAP_FAILED) {
fprintf(stderr, "failed to mmap %s: %s\n", devname,
strerror(errno));
exit(1);
}
}
else {
addr = valloc(block_size);
if (!addr) {
fprintf(stderr, "failed to allocate: %s\n", strerror(errno));
exit(1);
}
}
assert(fd != NULL);
*fd = sg_fd;
return addr;
}
void cleanup_addr_fd(void* addr, size_t size, int fd, int mmap)
{
if (addr) {
if (mmap)
munmap(addr, size);
else
free(addr);
}
close(fd);
}
void prepare_read16_cdb(size_t lba, size_t block_count, unsigned char
scsi_cmd[])
{
// initialize the scsi_cmd buffer
//
scsi_cmd[0] = (unsigned char)(0x88); /* READ 16 opcode */
scsi_cmd[2] = (unsigned char)((lba >> 56) & 0xff); /* lba */
scsi_cmd[3] = (unsigned char)((lba >> 48) & 0xff);
scsi_cmd[4] = (unsigned char)((lba >> 40) & 0xff);
scsi_cmd[5] = (unsigned char)((lba >> 32) & 0xff);
scsi_cmd[6] = (unsigned char)((lba >> 24) & 0xff);
scsi_cmd[7] = (unsigned char)((lba >> 16) & 0xff);
scsi_cmd[8] = (unsigned char)((lba >> 8) & 0xff);
scsi_cmd[9] = (unsigned char)(lba & 0xff);
scsi_cmd[10] = (unsigned char)((block_count >> 24) & 0xff); /*
block count */
scsi_cmd[11] = (unsigned char)((block_count >> 16) & 0xff);
scsi_cmd[12] = (unsigned char)((block_count >> 8) & 0xff);
scsi_cmd[13] = (unsigned char)(block_count & 0xff);
}
void scsi_read_block(const char* device, size_t lba, int fmmap, int fmmap_bug)
{
struct sg_io_hdr hdr;
unsigned char cdb[16];
unsigned char scsi_sense[96];
int fd = 0;
void* addr = NULL;
memset(cdb, 0, sizeof cdb);
memset(&hdr, 0, sizeof hdr);
memset(scsi_sense, 0, sizeof scsi_sense);
addr = prepare_addr_fd(device, 8192, &fd, fmmap);
prepare_read16_cdb(lba, 1, cdb);
hdr.interface_id = 'S';
hdr.dxfer_direction = SG_DXFER_FROM_DEV;
hdr.iovec_count = 0;
hdr.dxfer_len = 512;
hdr.mx_sb_len = sizeof scsi_sense;
hdr.sbp = scsi_sense;
hdr.timeout = 30000;
hdr.pack_id = 0;
hdr.usr_ptr = 0;
hdr.cmdp = cdb;
hdr.cmd_len = sizeof(cdb);
if (fmmap) {
hdr.flags = 4;
// dxferp is null unless we want to recreate the bug
if (fmmap_bug)
hdr.dxferp = addr;
}
else {
hdr.dxferp = addr;
}
if (ioctl(fd, SG_IO, &hdr) < 0) {
fprintf(stderr, "ioctl failed: %s\n", strerror(errno));
exit(1);
}
// pipe to od or hexdump
//
write(STDOUT_FILENO, addr, 64);
cleanup_addr_fd(addr, 8192, fd, fmmap);
}
int main(int argc, char* argv[])
{
const char* device = NULL;
ssize_t lba = -1;
int fmmap = 0;
int fmmap_bug = 0;
int opt;
const char* help_str =
"Usage: sg_mmap_read -d /dev/sgNNN -l <LBA> [-m -b]\n\n"
"Use -m to use mmap IO, use -b to check if dxferp is ignored\n"
"Redirect printing to od or hexdump\n";
if (argc == 1) {
puts(help_str);
return 0;
}
while ((opt = getopt(argc, argv, "d:l:mbh")) != -1) {
switch (opt) {
case 'd':
device = strdup(optarg);
break;
case 'l':
lba = atol(optarg);
break;
case 'm':
fmmap = 1;
break;
case 'b':
fmmap_bug = 1;
break;
case 'h':
puts(help_str);
return 0;
default:
return 1;
}
}
if (!device || lba == -1) {
fprintf(stderr, "command line error: missing device or lba");
return 1;
}
scsi_read_block(device, lba, fmmap, fmmap_bug);
return 0;
}
2016-11-21 2:04 GMT+02:00 Laurence Oberman <loberman@xxxxxxxxxx>:
>
>
> ----- Original Message -----
>> From: "Eyal Ben David" <bdeyal@xxxxxxxxx>
>> To: linux-scsi@xxxxxxxxxxxxxxx
>> Sent: Sunday, November 20, 2016 11:02:49 AM
>> Subject: SG does not ignore dxferp (direct io + mmap)
>>
>> Hi all,
>>
>> We have some IO utility that perform the IOs using sg and direct io with
>> mmap.
>> Our current systems are Ubuntu 14.04, RHEL 6,7
>> The IO utility always set dxferp to either the address or mmap of
>> other allocation (valloc)
>> Setting dxferp was harmless since SG is supposed to ignore the address
>> if mmap IO is selected.
>> When porting to Ubuntu 16.04, we had a corruption problem - first byte
>> of a read task is always 0.
>> When setting dxferp as NULL the corruption does not occur any more.
>> This is a regression and not according to SCSI generic documentation.
>>
>> I wrote a small program that shows the change:
>>
>> Read indirect (no mmap), lba=0:
>> =======================
>> $ ./sg_mmap_read -d /dev/sg0 -l 0
>> 0000000 eb 63 90 10 8e d0 bc 00 b0 b8 00 00 8e d8 8e c0
>>
>> Read with mmap, lba=0, dxferp=NULL:
>> ============================
>> $ ./sg_mmap_read -d /dev/sg0 -l 0 -m
>> 0000000 eb 63 90 10 8e d0 bc 00 b0 b8 00 00 8e d8 8e c0
>>
>> Read with mmap, lba=0, dxferp=address from mmap
>> ======================================
>> $ ./sg_mmap_read -d /dev/sg0 -l 0 -m -b
>> 0000000 00 63 90 10 8e d0 bc 00 b0 b8 00 00 8e d8 8e c0
>>
>> On the older systems all results are the same.
>>
>> Thanks for any answer!
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>
> Hello
>
> Given that we cannot see what your utility (sg_mmap_read) is doing, can we get the source for that or an strace of your test here.
> I am sure Doug will then be able to help you.
>
> Thanks
> Laurence
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