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dm flakey: add drop_writes

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Add 'drop_writes' option to drop writes silently while the
device is 'down'.  Reads are not touched.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mike Snitzer 2011-08-02 12:32:05 +01:00 committed by Alasdair G Kergon
parent dfd068b01f
commit b26f5e3d71
2 changed files with 79 additions and 15 deletions
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29
Documentation/device-mapper/dm-flakey.txt
View File

@ -1,17 +1,34 @@
dm-flakey
=========
This target is the same as the linear target except that it returns I/O
errors periodically. It's been found useful in simulating failing
devices for testing purposes.
This target is the same as the linear target except that it exhibits
unreliable behaviour periodically. It's been found useful in simulating
failing devices for testing purposes.
Starting from the time the table is loaded, the device is available for
<up interval> seconds, then returns errors for <down interval> seconds,
and then this cycle repeats.
<up interval> seconds, then exhibits unreliable behaviour for <down
interval> seconds, and then this cycle repeats.
Parameters: <dev path> <offset> <up interval> <down interval>
Also, consider using this in combination with the dm-delay target too,
which can delay reads and writes and/or send them to different
underlying devices.
Table parameters
----------------
<dev path> <offset> <up interval> <down interval> \
[<num_features> [<feature arguments>]]
Mandatory parameters:
<dev path>: Full pathname to the underlying block-device, or a
"major:minor" device-number.
<offset>: Starting sector within the device.
<up interval>: Number of seconds device is available.
<down interval>: Number of seconds device returns errors.
Optional feature parameters:
If no feature parameters are present, during the periods of
unreliability, all I/O returns errors.
drop_writes:
All write I/O is silently ignored.
Read I/O is handled correctly.

65
drivers/md/dm-flakey.c
View File

@ -25,16 +25,22 @@ struct flakey_c {
sector_t start;
unsigned up_interval;
unsigned down_interval;
unsigned long flags;
};
static int parse_features(struct dm_arg_set *as, struct dm_target *ti)
enum feature_flag_bits {
DROP_WRITES
};
static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
struct dm_target *ti)
{
int r;
unsigned argc;
const char *arg_name;
static struct dm_arg _args[] = {
{0, 0, "Invalid number of feature args"},
{0, 1, "Invalid number of feature args"},
};
/* No feature arguments supplied. */
@ -49,6 +55,18 @@ static int parse_features(struct dm_arg_set *as, struct dm_target *ti)
arg_name = dm_shift_arg(as);
argc--;
/*
* drop_writes
*/
if (!strcasecmp(arg_name, "drop_writes")) {
if (test_and_set_bit(DROP_WRITES, &fc->flags)) {
ti->error = "Feature drop_writes duplicated";
return -EINVAL;
}
continue;
}
ti->error = "Unrecognised flakey feature requested";
r = -EINVAL;
}
@ -59,6 +77,9 @@ static int parse_features(struct dm_arg_set *as, struct dm_target *ti)
/*
* Construct a flakey mapping:
* <dev_path> <offset> <up interval> <down interval> [<#feature args> [<arg>]*]
*
* Feature args:
* [drop_writes]
*/
static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
@ -81,7 +102,7 @@ static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
return -EINVAL;
}
fc = kmalloc(sizeof(*fc), GFP_KERNEL);
fc = kzalloc(sizeof(*fc), GFP_KERNEL);
if (!fc) {
ti->error = "Cannot allocate linear context";
return -ENOMEM;
@ -114,7 +135,7 @@ static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
goto bad;
}
r = parse_features(&as, ti);
r = parse_features(&as, fc, ti);
if (r)
goto bad;
@ -162,12 +183,31 @@ static int flakey_map(struct dm_target *ti, struct bio *bio,
{
struct flakey_c *fc = ti->private;
unsigned elapsed;
unsigned rw;
/* Are we alive ? */
elapsed = (jiffies - fc->start_time) / HZ;
if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval)
return -EIO;
if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval) {
rw = bio_data_dir(bio);
/*
* Drop writes. Map reads as normal.
*/
if (test_bit(DROP_WRITES, &fc->flags)) {
if (rw == WRITE) {
bio_endio(bio, 0);
return DM_MAPIO_SUBMITTED;
}
goto map_bio;
}
/*
* Default setting errors all I/O.
*/
return -EIO;
}
map_bio:
flakey_map_bio(ti, bio);
return DM_MAPIO_REMAPPED;
@ -176,7 +216,9 @@ static int flakey_map(struct dm_target *ti, struct bio *bio,
static int flakey_status(struct dm_target *ti, status_type_t type,
char *result, unsigned int maxlen)
{
unsigned sz = 0;
struct flakey_c *fc = ti->private;
unsigned drop_writes;
switch (type) {
case STATUSTYPE_INFO:
@ -184,9 +226,14 @@ static int flakey_status(struct dm_target *ti, status_type_t type,
break;
case STATUSTYPE_TABLE:
snprintf(result, maxlen, "%s %llu %u %u", fc->dev->name,
(unsigned long long)fc->start, fc->up_interval,
fc->down_interval);
DMEMIT("%s %llu %u %u ", fc->dev->name,
(unsigned long long)fc->start, fc->up_interval,
fc->down_interval);
drop_writes = test_bit(DROP_WRITES, &fc->flags);
DMEMIT("%u ", drop_writes);
if (drop_writes)
DMEMIT("drop_writes ");
break;
}
return 0;