Hi,
I have a question about algorithm used in dmraid to retrieve the
serial number from the scsi device:
lib/device/scsi.c:
77 /*
78 * Retrieve SCSI serial number.
79 */
80 #define MAX_RESPONSE_LEN 255
81 int
82 get_scsi_serial(struct lib_context *lc, int fd, struct dev_info *di,
83 enum ioctl_type type)
84 {
85 int ret = 0;
86 size_t actual_len;
87 unsigned char *response;
88 /*
89 * Define ioctl function and offset into response buffer of serial
90 * string length field (serial string follows length field immediately)
91 */
92 struct {
93 int (*ioctl_func) (int, unsigned char *, size_t);
94 unsigned int start;
95 } param[] = {
96 { sg_inquiry, 3},
97 { old_inquiry, 11},
98 }, *p = (SG == type) ? param : param + 1;
99
100 if (!(response = dbg_malloc(MAX_RESPONSE_LEN)))
101 return 0;
102
103 actual_len = p->start + 1;
104 if ((ret = (p->ioctl_func(fd, response, actual_len)))) {
105 size_t serial_len = (size_t) response[p->start];
106
107 if (serial_len > actual_len) {
108 actual_len += serial_len;
109 ret = p->ioctl_func(fd, response, actual_len);
110 }
111
112 ret = ret &&
113 (di->serial = dbg_strdup(remove_white_space (lc, (char *) &response[p->start + 1], serial_len)));
114 }
If type == SG, this function uses two SG_IO ioctls() to retrieve the serial number.
First with response buffer length set to 4 (line 104), which is just enough to get the serial
number length, which is later used to set the length of buffer for the second ioctl() (line 109).
Why is this? Why not use sufficiently long buffer (MAX_RESPONSE_LEN) right with the first ioctl()?
I'm asking this because I've encountered a device which requires the buffer to be long
enough to store the serial number, otherwise the SCSI inquiry command timeouts [*]. If this
happens, not only that it gets stuck for some time, but also the response buffer from the first
ioctl contains all zeros, so serial_len on line 105 is set to 0 and condition on line
107 is false -> second ioctl() is not executed...
[*] I know this is likely a bug outside dmraid.
I'd really appreciate if someone could shed some light into why it is done this way.
Thanks in advance,
Petr
--
Petr Uzel
IRC: ptr_uzl @ freenode
Attachment:
pgp6GJxcaXdZw.pgp
Description: PGP signature
_______________________________________________ Ataraid-list mailing list Ataraid-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ataraid-list
