On Tue, Jul 16, 2013 at 09:12:55AM +0200, Hannes Reinecke wrote:
> There are several constraints when setting fast_io_fail and
> dev_loss_tmo.
> dev_loss_tmo will be capped automatically when fast_io_fail is
> not set. And fast_io_fail can not be raised beyond dev_loss_tmo.
>
> So to increase dev_loss_tmo and fast_io_fail we first need
> to increase dev_loss_tmo to the given fast_io_fail
> setting, then set fast_io_fail, and then set dev_loss_tmo
> to the final setting.
This patch seems kind of convoluted to me, and even with the fix to
temporarily set dev_loss_tmo to one greater than fast_io_fail_tmo,
there is still a broken case
If you currently have:
fast_io_fail_tmo off
dev_loss_tmo <something_less_than_600>
and you want
fast_io_fail_tmo 600
dev_loss_tmo <something_greater_than_600>
This will fail, since it will try to set dev_loss_tmo to 601 with
fast_io_fail_tmo set to off (Granted, I doubt that 600 is a
popular fast_io_fail_tmo value).
But in the general case, If you aren't turning off fast_io_fail_tmo and
the current dev_loss_tmo is greater than the target fast_io_fail_tmo
(this seems like it is the most common case), you unecessarily go through
the work of first setting dev_loss_tmo to its current value.
if (mpp->fast_io_fail != MP_FAST_IO_FAIL_UNSET &&
mpp->fast_io_fail != MP_FAST_IO_FAIL_ZERO &&
mpp->fast_io_fail != MP_FAST_IO_FAIL_OFF) {
/* Check if we need to temporarily increase dev_loss_tmo
* */
ret = sysfs_attr_get_value(rport_dev, "dev_loss_tmo",
value, 16);
<SNIP>
}
if (strlen(value)) {
ret = sysfs_attr_set_value(rport_dev, "dev_loss_tmo",
value, strlen(value));
I have a patch that solves this issue differently. It still checks
dev_loss_tmo, but it always sets fast_io_fail_tmo first. If the target
fast_io_fail_tmo is greater than or equal to the current dev_loss_tmo,
it sets fast_io_fail_tmo to one less than the current dev_loss_tmo.
This always works, since the lowest value possible for dev_loss_tmo is 1
and the lowest value possible for fast_io_fail_tmo is 0. Then it sets
dev_loss_tmo. Finally, if necessary, it sets fast_io_fail_tmo to its
final value.
I'll push that shortly.
-Ben
>
> Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
> ---
> libmultipath/discovery.c | 66 +++++++++++++++++++++++++++++++++++++-----------
> libmultipath/sysfs.c | 64 ++++++++++++++++++++++++++++++++++++++++++++--
> libmultipath/sysfs.h | 2 ++
> 3 files changed, 115 insertions(+), 17 deletions(-)
>
> diff --git a/libmultipath/discovery.c b/libmultipath/discovery.c
> index 26983ca..18f72ec 100644
> --- a/libmultipath/discovery.c
> +++ b/libmultipath/discovery.c
> @@ -317,6 +317,7 @@ sysfs_set_rport_tmo(struct multipath *mpp, struct path *pp)
> struct udev_device *rport_dev = NULL;
> char value[11];
> char rport_id[32];
> + unsigned long long tmo;
>
> sprintf(rport_id, "rport-%d:%d-%d",
> pp->sg_id.host_no, pp->sg_id.channel, pp->sg_id.transport_id);
> @@ -330,23 +331,51 @@ sysfs_set_rport_tmo(struct multipath *mpp, struct path *pp)
> condlog(4, "target%d:%d:%d -> %s", pp->sg_id.host_no,
> pp->sg_id.channel, pp->sg_id.scsi_id, rport_id);
>
> - snprintf(value, 11, "%u", mpp->dev_loss);
> - if (mpp->dev_loss &&
> - sysfs_attr_set_value(rport_dev, "dev_loss_tmo", value, 11) <= 0) {
> - if ((mpp->fast_io_fail == MP_FAST_IO_FAIL_UNSET ||
> - mpp->fast_io_fail == MP_FAST_IO_FAIL_OFF)
> - && mpp->dev_loss > 600) {
> - condlog(3, "%s: limiting dev_loss_tmo to 600, since "
> - "fast_io_fail is not set", mpp->alias);
> - snprintf(value, 11, "%u", 600);
> - if (sysfs_attr_set_value(rport_dev, "dev_loss_tmo",
> - value, 11) <= 0)
> - condlog(0, "%s failed to set dev_loss_tmo",
> - mpp->alias);
> + /*
> + * This is tricky.
> + * dev_loss_tmo will be limited to 600 if fast_io_fail
> + * is _not_ set.
> + * fast_io_fail will be limited by the current dev_loss_tmo
> + * setting.
> + * So to get everything right we first need to increase
> + * dev_loss_tmo to the fast_io_fail setting (if present),
> + * then set fast_io_fail, and _then_ set dev_loss_tmo
> + * to the correct value.
> + */
> + value[0] = '\0';
> + if (mpp->fast_io_fail != MP_FAST_IO_FAIL_UNSET &&
> + mpp->fast_io_fail != MP_FAST_IO_FAIL_OFF) {
> + /* Check if we need to temporarily increase dev_loss_tmo */
> + if (sysfs_attr_get_value(rport_dev, "dev_loss_tmo",
> + value, 16) <= 0) {
> + condlog(0, "%s: failed to read dev_loss_tmo value, "
> + "error %d", pp->dev, errno);
> + goto out;
> + }
> + if (sscanf(value, "%llu\n", &tmo) != 1) {
> + condlog(0, "%s: Cannot parse dev_loss_tmo "
> + "attribute '%s'",pp->dev, value);
> goto out;
> }
> + if (mpp->fast_io_fail >= tmo) {
> + snprintf(value, 11, "%u", mpp->fast_io_fail);
> + } else {
> + tmo = 0;
> + }
> + } else if (mpp->dev_loss > 600) {
> + condlog(3, "%s: limiting dev_loss_tmo to 600, since "
> + "fast_io_fail is not set", pp->dev);
> + snprintf(value, 11, "%u", 600);
> + } else {
> + snprintf(value, 11, "%u", mpp->dev_loss);
> }
> - if (mpp->fast_io_fail != MP_FAST_IO_FAIL_UNSET){
> + if (strlen(value) &&
> + sysfs_attr_set_value(rport_dev, "dev_loss_tmo", value, 11) <= 0) {
> + condlog(0, "%s failed to set dev_loss_tmo",
> + mpp->alias);
> + goto out;
> + }
> + if (mpp->fast_io_fail != MP_FAST_IO_FAIL_UNSET) {
> if (mpp->fast_io_fail == MP_FAST_IO_FAIL_OFF)
> sprintf(value, "off");
> else if (mpp->fast_io_fail == MP_FAST_IO_FAIL_ZERO)
> @@ -359,6 +388,13 @@ sysfs_set_rport_tmo(struct multipath *mpp, struct path *pp)
> mpp->alias);
> }
> }
> + if (tmo > 0) {
> + snprintf(value, 11, "%u", mpp->dev_loss);
> + if (sysfs_attr_set_value(rport_dev, "dev_loss_tmo",
> + value, 11) <= 0)
> + condlog(0, "%s failed to set dev_loss_tmo",
> + mpp->alias);
> + }
> out:
> udev_device_unref(rport_dev);
> }
> @@ -394,7 +430,7 @@ sysfs_set_session_tmo(struct multipath *mpp, struct path *pp)
> } else {
> snprintf(value, 11, "%u", mpp->fast_io_fail);
> if (sysfs_attr_set_value(session_dev, "recovery_tmo",
> - value, 11)) {
> + value, 11) <= 0) {
> condlog(3, "%s: Failed to set recovery_tmo, "
> " error %d", pp->dev, errno);
> }
> diff --git a/libmultipath/sysfs.c b/libmultipath/sysfs.c
> index d33747f..22b73b1 100644
> --- a/libmultipath/sysfs.c
> +++ b/libmultipath/sysfs.c
> @@ -38,6 +38,62 @@
> #include "debug.h"
> #include "devmapper.h"
>
> +/*
> + * When we modify an attribute value we cannot rely on libudev for now,
> + * as libudev lacks the capability to update an attribute value.
> + * So for modified attributes we need to implement our own function.
> + */
> +ssize_t sysfs_attr_get_value(struct udev_device *dev, const char *attr_name,
> + char * value, size_t value_len)
> +{
> + char devpath[PATH_SIZE];
> + struct stat statbuf;
> + int fd;
> + ssize_t size = -1;
> +
> + if (!dev || !attr_name || !value)
> + return 0;
> +
> + snprintf(devpath, PATH_SIZE, "%s/%s", udev_device_get_syspath(dev),
> + attr_name);
> + condlog(4, "open '%s'", devpath);
> + if (stat(devpath, &statbuf) != 0) {
> + condlog(4, "stat '%s' failed: %s", devpath, strerror(errno));
> + return 0;
> + }
> +
> + /* skip directories */
> + if (S_ISDIR(statbuf.st_mode)) {
> + condlog(4, "%s is a directory", devpath);
> + return 0;
> + }
> +
> + /* skip non-writeable files */
> + if ((statbuf.st_mode & S_IRUSR) == 0) {
> + condlog(4, "%s is not readable", devpath);
> + return 0;
> + }
> +
> + /* read attribute value */
> + fd = open(devpath, O_RDONLY);
> + if (fd < 0) {
> + condlog(4, "attribute '%s' can not be opened: %s",
> + devpath, strerror(errno));
> + return 0;
> + }
> + size = read(fd, value, value_len);
> + if (size < 0) {
> + condlog(4, "read from %s failed: %s", devpath, strerror(errno));
> + size = 0;
> + } else if (size == value_len) {
> + condlog(4, "overflow while reading from %s", devpath);
> + size = 0;
> + }
> +
> + close(fd);
> + return size;
> +}
> +
> ssize_t sysfs_attr_set_value(struct udev_device *dev, const char *attr_name,
> char * value, size_t value_len)
> {
> @@ -58,12 +114,16 @@ ssize_t sysfs_attr_set_value(struct udev_device *dev, const char *attr_name,
> }
>
> /* skip directories */
> - if (S_ISDIR(statbuf.st_mode))
> + if (S_ISDIR(statbuf.st_mode)) {
> + condlog(4, "%s is a directory", devpath);
> return 0;
> + }
>
> /* skip non-writeable files */
> - if ((statbuf.st_mode & S_IWUSR) == 0)
> + if ((statbuf.st_mode & S_IWUSR) == 0) {
> + condlog(4, "%s is not writeable", devpath);
> return 0;
> + }
>
> /* write attribute value */
> fd = open(devpath, O_WRONLY);
> diff --git a/libmultipath/sysfs.h b/libmultipath/sysfs.h
> index 13d7545..34f3e00 100644
> --- a/libmultipath/sysfs.h
> +++ b/libmultipath/sysfs.h
> @@ -7,6 +7,8 @@
>
> ssize_t sysfs_attr_set_value(struct udev_device *dev, const char *attr_name,
> char * value, size_t value_len);
> +ssize_t sysfs_attr_get_value(struct udev_device *dev, const char *attr_name,
> + char * value, size_t value_len);
> int sysfs_get_size (struct path *pp, unsigned long long * size);
> int sysfs_check_holders(char * check_devt, char * new_devt);
> #endif
> --
> 1.7.12.4
>
> --
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> https://www.redhat.com/mailman/listinfo/dm-devel
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