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/* ddlpa
Implementation of Delicate Device Locking Protocol level A.
Copyright (C) 2007 Thomas Schmitt <scdbackup@gmx.net>
Provided under any of the following licenses: GPL, LGPL, BSD. Choose one.
Compile as test program:
cc -g -Wall \
-D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE=1 -D_LARGEFILE64_SOURCE \
-DDDLPA_C_STANDALONE -o ddlpa ddlpa.c
The system macros enable 64-bit off_t and open(2) flag O_LARGEFILE, which
are not absolutely necessary but explicitly take into respect that
our devices can offer more than 2 GB of addressable data.
Run test program:
./ddlpa /dev/sr0 15
./ddlpa 0,0,0 15
*/
#ifdef HAVE_CONFIG_H
#include "../config.h"
#endif
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <scsi/scsi.h>
/* All callers of ddlpa must do this */
#include "ddlpa.h"
/* 1 = Enable progress message on stderr, 0 = normal silent operation */
static int ddlpa_debug_mode = 1;
/* #define _GNU_SOURCE or _LARGEFILE64_SOURCE to get real O_LARGEFILE */
#ifndef O_LARGEFILE
#define O_LARGEFILE 0
#endif
#ifndef O_BINARY
#define O_BINARY 0
#endif
/* ----------------------- private -------------------- */
static int ddlpa_new(struct ddlpa_lock **lck, int o_flags, int ddlpa_flags)
{
int i;
struct ddlpa_lock *o;
o = *lck = (struct ddlpa_lock *) malloc(sizeof(struct ddlpa_lock));
if (o == NULL)
return ENOMEM;
for (i = 0; i < sizeof(struct ddlpa_lock); i++)
((char *) o)[i] = 0;
o->path = NULL;
o->fd = -1;
for (i = 0; i < DDLPA_MAX_SIBLINGS; i++)
o->sibling_fds[i] = -1;
o->errmsg = NULL;
o->o_flags = o_flags;
o->ddlpa_flags = ddlpa_flags;
return 0;
}
static int ddlpa_enumerate(struct ddlpa_lock *o, int *idx,
char path[DDLPA_MAX_STD_LEN + 1])
{
if (*idx < 0)
*idx = 0;
if (*idx < 26)
sprintf(path, "/dev/hd%c", 'a' + *idx);
else if (*idx < 256 + 26)
sprintf(path, "/dev/sr%d", *idx - 26);
else if (*idx < 2 * 256 + 26)
sprintf(path, "/dev/scd%d", *idx - 256 - 26);
else if (*idx < 3 * 256 + 26)
sprintf(path, "/dev/sg%d", *idx - 2 * 256 - 26);
else
return 1;
(*idx)++;
return 0;
}
static int ddlpa_std_by_rdev(struct ddlpa_lock *o)
{
int idx = 0;
char try_path[DDLPA_MAX_STD_LEN+1];
struct stat path_stbuf, try_stbuf;
if (!o->path_is_valid)
return EFAULT;
if (stat(o->path, &path_stbuf) == -1)
return errno;
while (ddlpa_enumerate(o, &idx, try_path) == 0) {
if (stat(try_path, &try_stbuf) == -1)
continue;
if (path_stbuf.st_rdev != try_stbuf.st_rdev)
continue;
strcpy(o->std_path, try_path);
if (ddlpa_debug_mode)
fprintf(stderr,
"DDLPA_DEBUG: ddlpa_std_by_rdev(\"%s\") = \"%s\"\n",
o->path, o->std_path);
return 0;
}
return ENOENT;
}
/* Caution : these tests are valid only with standard paths */
static int ddlpa_is_scsi(struct ddlpa_lock *o, char *path)
{
return (strncmp(path, "/dev/s", 6) == 0);
}
static int ddlpa_is_sg(struct ddlpa_lock *o, char *path)
{
return (strncmp(path, "/dev/sg", 7) == 0);
}
static int ddlpa_is_sr(struct ddlpa_lock *o, char *path)
{
return (strncmp(path, "/dev/sr", 7) == 0);
}
static int ddlpa_is_scd(struct ddlpa_lock *o, char *path)
{
return (strncmp(path, "/dev/scd", 8) == 0);
}
static int ddlpa_fcntl_lock(struct ddlpa_lock *o, int fd, int l_type)
{
struct flock lockthing;
int ret;
memset(&lockthing, 0, sizeof(lockthing));
lockthing.l_type = l_type;
lockthing.l_whence = SEEK_SET;
lockthing.l_start = 0;
lockthing.l_len = 0;
ret = fcntl(fd, F_SETLK, &lockthing);
if (ret == -1)
return EBUSY;
return 0;
}
static int ddlpa_occupy(struct ddlpa_lock *o, char *path, int *fd,
int no_o_excl)
{
int ret, o_flags, o_rw, l_type;
char *o_rwtext;
o_flags = o->o_flags | O_NDELAY | O_BINARY;
if(!no_o_excl)
o_flags |= O_EXCL;
o_rw = (o_flags) & (O_RDONLY | O_WRONLY | O_RDWR);
o_rwtext = (o_rw == O_RDONLY ? "O_RDONLY" :
(o_rw == O_WRONLY ? "O_WRONLY" :
(o_rw == O_RDWR ? "O_RDWR " : "O_?rw-mode?")));
*fd = open(path, o_flags);
if (*fd == -1) {
o->errmsg = malloc(strlen(path)+160);
if (o->errmsg)
sprintf(o->errmsg,
"Failed to open %s | O_NDELAY %s: '%s'",
o_rwtext,
(o_flags & O_EXCL ? "| O_EXCL " : ""), path);
return (errno ? errno : EBUSY);
}
if (o_rw == O_RDWR || o_rw == O_WRONLY)
l_type = F_WRLCK;
else
l_type = F_RDLCK;
ret = ddlpa_fcntl_lock(o, *fd, l_type);
if (ret) {
o->errmsg = malloc(strlen(path)+160);
if (o->errmsg)
sprintf(o->errmsg,
"Failed to lock fcntl(F_WRLCK) : '%s'",path);
close(*fd);
*fd = -1;
return ret;
}
if (ddlpa_debug_mode)
fprintf(stderr, "DDLPA_DEBUG: ddlpa_occupy() %s %s: '%s'\n",
o_rwtext,
(no_o_excl ? " " : "O_EXCL "), path);
return 0;
}
static int ddlpa_obtain_scsi_adr(struct ddlpa_lock *o, char *path,
int *bus, int *host, int *channel, int *id, int *lun)
{
int fd, ret, open_mode = O_RDONLY | O_NDELAY | O_BINARY;
struct my_scsi_idlun {
int x;
int host_unique_id;
};
struct my_scsi_idlun idlun;
fd = open(path, open_mode);
if (fd == -1)
return (errno ? errno : EBUSY);
if (ioctl(fd, SCSI_IOCTL_GET_BUS_NUMBER, bus) == -1)
*bus = -1;
ret = ioctl(fd, SCSI_IOCTL_GET_IDLUN, &idlun);
close(fd);
if (ret == -1)
return (errno ? errno : EIO);
*host = (idlun.x >> 24) & 255;
*channel = (idlun.x >> 16) & 255;
*id = (idlun.x) & 255;
*lun = (idlun.x >> 8 ) & 255;
return 0;
}
static int ddlpa_collect_siblings(struct ddlpa_lock *o)
{
int idx = 0, ret, have_sg = 0, have_sr = 0, have_scd = 0;
dev_t path_dev;
ino_t path_inode;
struct stat stbuf;
char *path, try_path[DDLPA_MAX_STD_LEN+1];
int t_bus, t_host, t_channel, t_id, t_lun;
if (o->ddlpa_flags & DDLPA_OPEN_GIVEN_PATH)
path = o->path;
else
path = o->std_path;
if (path[0] == 0 || o->num_siblings != 0)
return EFAULT;
if (!ddlpa_is_scsi(o, o->std_path))
return EFAULT;
if (stat(path, &stbuf) == -1)
return errno;
path_inode = stbuf.st_ino;
path_dev = stbuf.st_dev;
o->rdev = stbuf.st_rdev;
o->dev = stbuf.st_dev;
o->ino = stbuf.st_ino;
ret = ddlpa_obtain_scsi_adr(o, path,
&(o->bus), &(o->host), &(o->channel),
&(o->id), &(o->lun));
if (ret) {
o->errmsg = strdup(
"Cannot obtain SCSI parameters host,channel,id,lun");
return ret;
}
o->hcilb_is_valid = 1;
while (ddlpa_enumerate(o, &idx, try_path) == 0) {
if (!ddlpa_is_scsi(o, try_path))
continue;
if (stat(try_path, &stbuf) == -1)
continue;
ret = ddlpa_obtain_scsi_adr(o, try_path,
&t_bus, &t_host, &t_channel, &t_id, &t_lun);
if (ret) {
/* >>> interpret error, memorize busy, no permission */
continue;
}
if (t_host != o->host || t_channel != o->channel ||
t_id != o->id || t_lun != o->lun)
continue;
if (o->num_siblings >= DDLPA_MAX_SIBLINGS) {
o->errmsg =
strdup("Too many matching device files found");
return ERANGE;
}
if (ddlpa_is_sg(o, try_path))
have_sg = 1;
else if (ddlpa_is_sr(o, try_path))
have_sr = 1;
else if (ddlpa_is_scd(o, try_path))
have_scd = 1;
strcpy(o->sibling_paths[o->num_siblings], try_path);
o->sibling_rdevs[o->num_siblings] = stbuf.st_rdev;
o->sibling_devs[o->num_siblings] = stbuf.st_dev;
o->sibling_inodes[o->num_siblings] = stbuf.st_ino;
if (ddlpa_debug_mode)
fprintf(stderr,
"DDLPA_DEBUG: ddlpa_collect_siblings() found \"%s\"\n",
try_path);
(o->num_siblings)++;
}
if (have_sg && have_sr && have_scd)
return 0;
if (o->ddlpa_flags & DDLPA_ALLOW_MISSING_SGRCD)
return 0;
o->errmsg = strdup("Did not find enough siblings");
/* >>> add more info about busy and forbidden paths */
return EBUSY;
}
static int ddlpa_std_by_btl(struct ddlpa_lock *o)
{
int idx = 0, ret;
char try_path[DDLPA_MAX_STD_LEN+1];
int t_bus, t_host, t_channel, t_id, t_lun;
if (!o->inbtl_is_valid)
return EFAULT;
while (ddlpa_enumerate(o, &idx, try_path) == 0) {
if (!ddlpa_is_sr(o, try_path))
continue;
ret = ddlpa_obtain_scsi_adr(o, try_path,
&t_bus, &t_host, &t_channel, &t_id, &t_lun);
if (ret) {
/* >>> interpret error, memorize busy, no permission */
continue;
}
if (t_bus != o->in_bus || t_id != o->in_target ||
t_lun != o->in_lun)
continue;
strcpy(o->std_path, try_path);
if (ddlpa_debug_mode)
fprintf(stderr,
"DDLPA_DEBUG: ddlpa_std_by_btl(%d,%d,%d) = \"%s\"\n",
t_bus, t_id, t_lun, o->std_path);
return 0;
}
/* >>> add more info about busy and forbidden paths */
return ENOENT;
}
static int ddlpa_open_all(struct ddlpa_lock *o)
{
int i, j, ret, no_o_excl;
if (ddlpa_is_scsi(o, o->std_path)) {
ret = ddlpa_collect_siblings(o);
if (ret)
return ret;
for (i = 0; i < o->num_siblings; i++) {
/* Watch out for the main personality of the drive. */
/* No need to occupy identical path or softlink path */
if (o->sibling_devs[i] == o->dev &&
o->sibling_inodes[i] == o->ino)
continue;
/* There may be the same rdev but different inode. */
no_o_excl = (o->sibling_rdevs[i] == o->rdev);
/* Look for multiply registered device drivers with
distinct inodes. */
for (j = 0; j < i; j++) {
if (o->sibling_devs[j] == o->sibling_devs[i] &&
o->sibling_inodes[j] == o->sibling_inodes[i])
break;
if (o->sibling_rdevs[j] == o->sibling_rdevs[i])
no_o_excl = 1;
}
if (j < i)
continue; /* inode is already occupied */
ret = ddlpa_occupy(o, o->sibling_paths[i],
&(o->sibling_fds[i]), no_o_excl);
if (ret)
return ret;
}
}
if (o->ddlpa_flags & DDLPA_OPEN_GIVEN_PATH)
ret = ddlpa_occupy(o, o->path, &(o->fd), 0);
else
ret = ddlpa_occupy(o, o->std_path, &(o->fd), 0);
if (ret)
return ret;
/* >>> use fcntl() to adjust O_NONBLOCK */;
return 0;
}
/* ----------------------- public -------------------- */
int ddlpa_destroy(struct ddlpa_lock **lockbundle)
{
struct ddlpa_lock *o;
int i;
o= *lockbundle;
if (o == NULL)
return 0;
for (i = 0; i < o->num_siblings; i++)
if (o->sibling_fds[i] != -1)
close(o->sibling_fds[i]);
if(o->fd != -1)
close(o->fd);
if (o->path != NULL)
free(o->path);
if (o->errmsg != NULL)
free(o->errmsg);
free((char *) o);
*lockbundle = NULL;
return 0;
}
int ddlpa_lock_path(char *path, int o_flags, int ddlpa_flags,
struct ddlpa_lock **lockbundle, char **errmsg)
{
struct ddlpa_lock *o;
int ret;
*errmsg = NULL;
if (ddlpa_new(&o, o_flags, ddlpa_flags))
return ENOMEM;
*lockbundle = o;
o->path = strdup(path);
if (o->path == NULL)
return ENOMEM;
o->path_is_valid = 1;
ret = ddlpa_std_by_rdev(o);
if (ret) {
*errmsg = strdup(
"Cannot find equivalent of given path among standard paths");
return ret;
}
ret = ddlpa_open_all(o);
if (ret) {
*errmsg = o->errmsg;
o->errmsg = NULL;
ddlpa_destroy(&o);
}
return ret;
}
int ddlpa_lock_btl(int bus, int target, int lun,
int o_flags, int ddlpa_flags,
struct ddlpa_lock **lockbundle, char **errmsg)
{
struct ddlpa_lock *o;
int ret;
*errmsg = NULL;
ddlpa_flags &= ~DDLPA_OPEN_GIVEN_PATH;
if (ddlpa_new(&o, o_flags, ddlpa_flags))
return ENOMEM;
*lockbundle = o;
o->in_bus = bus;
o->in_target = target;
o->in_lun = lun;
o->inbtl_is_valid = 1;
ret = ddlpa_std_by_btl(o);
if (ret) {
*errmsg = strdup(
"Cannot find /dev/sr* with given Bus,Target,Lun");
return ret;
}
ret = ddlpa_open_all(o);
if (ret) {
*errmsg = o->errmsg;
o->errmsg = NULL;
ddlpa_destroy(&o);
return ret;
}
return 0;
}
#ifdef DDLPA_C_STANDALONE
/* ----------------------------- Test / Demo -------------------------- */
int main(int argc, char **argv)
{
struct ddlpa_lock *lck = NULL;
char *errmsg = NULL, *opened_path = NULL, *my_path = NULL;
int i, ret, fd = -1, duration = -1, bus = -1, target = -1, lun = -1;
if (argc < 3) {
usage:;
fprintf(stderr, "usage: %s device_path duration\n", argv[0]);
exit(1);
}
my_path = argv[1];
sscanf(argv[2], "%d", &duration);
if (duration < 0)
goto usage;
/* For our purpose, only O_RDWR is a suitable access mode.
But in order to allow experiments, o_flags are freely adjustable.
Warning: Do _not_ set an own O_EXCL flag with the following calls !
(This freedom to fail may get removed in a final version.)
*/
if (my_path[0] != '/' && my_path[0] != '.' &&
strchr(my_path, ',') != NULL) {
/*
cdrecord style dev=Bus,Target,Lun
*/
sscanf(my_path, "%d,%d,%d", &bus, &target, &lun);
ret = ddlpa_lock_btl(bus, target, lun, O_RDWR | O_LARGEFILE,
0, &lck, &errmsg);
} else {
/*
This substitutes for:
fd = open(my_path,
O_RDWR | O_EXCL | O_LARGEFILE | O_BINARY);
*/
ret = ddlpa_lock_path(my_path, O_RDWR | O_LARGEFILE,
0, &lck, &errmsg);
}
if (ret) {
fprintf(stderr, "Cannot exclusively open '%s'\n", my_path);
if (errmsg != NULL)
fprintf(stderr, "Reason given : %s\n",
errmsg);
free(errmsg);
fprintf(stderr, "Error condition : %d '%s'\n",
ret, strerror(ret));
exit(2);
}
fd = lck->fd;
printf("---------------------------------------------- Lock gained\n");
/* Use fd for the usual operations on the device depicted by my_path.
*/
/* This prints an overview of the impact of the lock */
if (lck->ddlpa_flags & DDLPA_OPEN_GIVEN_PATH)
opened_path = lck->path;
else
opened_path = lck->std_path;
printf("ddlpa: opened %s", opened_path);
if (strcmp(opened_path, lck->std_path) != 0)
printf(" (an alias of '%s')", lck->std_path);
printf("\n");
if (lck->num_siblings > 0) {
printf("ddlpa: opened siblings:");
for (i = 0; i < lck->num_siblings; i++)
if (lck->sibling_fds[i] != -1)
printf(" %s", lck->sibling_paths[i]);
printf("\n");
}
/* This example waits a while. So other lock candidates can collide. */
for (i = 0; i < duration; i++) {
sleep(1);
fprintf(stderr, "\rslept %d seconds of %d", i + 1, duration);
}
fprintf(stderr, "\n");
/* When finally done with the drive, this substitutes for:
close(fd);
*/
if (ddlpa_destroy(&lck)) {
/* Well, man 2 close says it can fail. */
exit(3);
}
exit(0);
}
#endif /* DDLPA_C_STANDALONE */