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[SCSI] st: raise device limit 

The device limit of 128 tape drives was established in 2003 as a
significant increase from the 8 tape drives allowed previously.

We're seeing customer sites that between a large number of drives
and multipath are discovering more than 128 devices and running
into problems.

Now that we're not stuck having to store a pointer in array
and aren't limited by kmalloc failing on higher order allocs we can
lift the limit to fill the entire minor range based on the number
of modes.

Based on the current code, that's 2^17 devices.

Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
This commit is contained in:
Jeff Mahoney 2012-08-18 15:20:41 -04:00 committed by James Bottomley
parent 26898afd67
commit 6ed33a4a0b
2 changed files with 3 additions and 5 deletions
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6
Documentation/scsi/st.txt
View File

@ -112,10 +112,8 @@ attempted).
MINOR NUMBERS
The tape driver currently supports 128 drives by default. This number
can be increased by editing st.h and recompiling the driver if
necessary. The upper limit is 2^17 drives if 4 modes for each drive
are used.
The tape driver currently supports up to 2^17 drives if 4 modes for
each drive are used.
The minor numbers consist of the following bit fields:

2
drivers/scsi/st.h
View File

@ -78,7 +78,7 @@ struct st_modedef {
#define ST_MODE_SHIFT (7 - ST_NBR_MODE_BITS)
#define ST_MODE_MASK ((ST_NBR_MODES - 1) << ST_MODE_SHIFT)
#define ST_MAX_TAPES 128
#define ST_MAX_TAPES (1 << (20 - (ST_NBR_MODE_BITS + 1)))
#define ST_MAX_TAPE_ENTRIES (ST_MAX_TAPES << (ST_NBR_MODE_BITS + 1))
/* The status related to each partition */