[PATCH 3/4] s390/dasd: Move device name formatting into separate function

Stefan Haberland
2025-11-26T16:06:43Z

From: Jan Höppner <hoeppner@linux.ibm.com>

The device name formatting can be generalized and made more readable
compared to the current state. SCSI already provides a generalized way
to format many devices in the same naming scheme as DASD does, which was
introduced with commit 3e1a7ff8a0a7 ("block: allow disk to have extended
device number").

Use this much cleaner code from drivers/scsi/sd.c to handle the legacy
naming scheme in DASD as a replacement for the current implementation.

For easier error handling for the new function, move the gendisk free
portion of dasd_gendisk_free() out into a new function dasd_gd_free().

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
---
drivers/s390/block/dasd_genhd.c | 80 ++++++++++++++++++++++-----------
1 file changed, 54 insertions(+), 26 deletions(-)

diff --git a/drivers/s390/block/dasd_genhd.c b/drivers/s390/block/dasd_genhd.c
index 28e92fad0ca1..6ee3d952412e 100644
--- a/drivers/s390/block/dasd_genhd.c
+++ b/drivers/s390/block/dasd_genhd.c
@@ -22,6 +22,7 @@

static unsigned int queue_depth = 32;
static unsigned int nr_hw_queues = 4;
+static void dasd_gd_free(struct gendisk *gdp);

module_param(queue_depth, uint, 0444);
MODULE_PARM_DESC(queue_depth, "Default queue depth for new DASD devices");
@@ -29,6 +30,37 @@ MODULE_PARM_DESC(queue_depth, "Default queue depth for new DASD devices");
module_param(nr_hw_queues, uint, 0444);
MODULE_PARM_DESC(nr_hw_queues, "Default number of hardware queues for new DASD devices");

+/*
+ * Set device name.
+ * dasda - dasdz : 26 devices
+ * dasdaa - dasdzz : 676 devices, added up = 702
+ * dasdaaa - dasdzzz : 17576 devices, added up = 18278
+ * dasdaaaa - dasdzzzz : 456976 devices, added up = 475252
+ */
+static int dasd_name_format(char *prefix, int index, char *buf, int buflen)
+{
+ const int base = 'z' - 'a' + 1;
+ char *begin = buf + strlen(prefix);
+ char *end = buf + buflen;
+ char *p;
+ int unit;
+
+ p = end - 1;
+ *p = '\0';
+ unit = base;
+ do {
+ if (p == begin)
+ return -EINVAL;
+ *--p = 'a' + (index % unit);
+ index = (index / unit) - 1;
+ } while (index >= 0);
+
+ memmove(begin, p, end - p);
+ memcpy(buf, prefix, strlen(prefix));
+
+ return 0;
+}
+
/*
* Allocate and register gendisk structure for device.
*/
@@ -45,11 +77,13 @@ int dasd_gendisk_alloc(struct dasd_block *block)
};
struct gendisk *gdp;
struct dasd_device *base;
- int len, rc;
+ unsigned int devindex;
+ int rc;

/* Make sure the minor for this device exists. */
base = block->base;
- if (base->devindex >= DASD_PER_MAJOR)
+ devindex = base->devindex;
+ if (devindex >= DASD_PER_MAJOR)
return -EBUSY;

block->tag_set.ops = &dasd_mq_ops;
@@ -69,31 +103,17 @@ int dasd_gendisk_alloc(struct dasd_block *block)

/* Initialize gendisk structure. */
gdp->major = DASD_MAJOR;
- gdp->first_minor = base->devindex << DASD_PARTN_BITS;
+ gdp->first_minor = devindex << DASD_PARTN_BITS;
gdp->minors = 1 << DASD_PARTN_BITS;
gdp->fops = &dasd_device_operations;

- /*
- * Set device name.
- * dasda - dasdz : 26 devices
- * dasdaa - dasdzz : 676 devices, added up = 702
- * dasdaaa - dasdzzz : 17576 devices, added up = 18278
- * dasdaaaa - dasdzzzz : 456976 devices, added up = 475252
- */
- len = sprintf(gdp->disk_name, "dasd");
- if (base->devindex > 25) {
- if (base->devindex > 701) {
- if (base->devindex > 18277)
- len += sprintf(gdp->disk_name + len, "%c",
- 'a'+(((base->devindex-18278)
- /17576)%26));
- len += sprintf(gdp->disk_name + len, "%c",
- 'a'+(((base->devindex-702)/676)%26));
- }
- len += sprintf(gdp->disk_name + len, "%c",
- 'a'+(((base->devindex-26)/26)%26));
+ rc = dasd_name_format("dasd", devindex, gdp->disk_name, sizeof(gdp->disk_name));
+ if (rc) {
+ DBF_DEV_EVENT(DBF_ERR, block->base,
+ "setting disk name failed, rc %d", rc);
+ dasd_gd_free(gdp);
+ return rc;
}
- len += sprintf(gdp->disk_name + len, "%c", 'a'+(base->devindex%26));

if (base->features & DASD_FEATURE_READONLY ||
test_bit(DASD_FLAG_DEVICE_RO, &base->flags))
@@ -111,15 +131,23 @@ int dasd_gendisk_alloc(struct dasd_block *block)
return 0;
}

+/*
+ * Free gendisk structure
+ */
+static void dasd_gd_free(struct gendisk *gd)
+{
+ del_gendisk(gd);
+ gd->private_data = NULL;
+ put_disk(gd);
+}
+
/*
* Unregister and free gendisk structure for device.
*/
void dasd_gendisk_free(struct dasd_block *block)
{
if (block->gdp) {
- del_gendisk(block->gdp);
- block->gdp->private_data = NULL;
- put_disk(block->gdp);
+ dasd_gd_free(block->gdp);
block->gdp = NULL;
blk_mq_free_tag_set(&block->tag_set);
}
--
2.51.0