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authorLogan Gunthorpe <logang@deltatee.com>2017-06-15 14:05:20 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-07-17 15:09:17 +0200
commita5d31a3f81c6fb13b381951bf6163444c0257e8b (patch)
tree07cbc6fc6029a492b2b6e7a4ec14c71fbe7a1744 /Documentation/admin-guide
parentf5ac3c49ff0b36d9b6a804b4b86efcaf27ba044b (diff)
downloadlinux-a5d31a3f81c6fb13b381951bf6163444c0257e8b.tar.bz2
char_dev: extend dynamic allocation of majors into a higher range
We've run into problems with running out of dynamicly assign char device majors particullarly on automated test systems with all-yes-configs. Roughly 40 dynamic assignments can be made with such kernels at this time while space is reserved for only 20. Currently, the kernel only prints a warning when dynamic allocation overflows the reserved region. And when this happens drivers that have fixed assignments can randomly fail depending on the order of initialization of other drivers. Thus, adding a new char device can cause unexpected failures in completely unrelated parts of the kernel. This patch solves the problem by extending dynamic major number allocations down from 511 once the 234-254 region fills up. Fixed majors already exist above 255 so the infrastructure to support high number majors is already in place. The patch reserves an additional 128 major numbers which should hopefully last us a while. Kernels that don't require more than 20 dynamic majors assigned (which is pretty typical) should not be affected by this change. Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Alan Cox <alan@linux.intel.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Linus Walleij <linus.walleij@linaro.org> Link: https://lkml.org/lkml/2017/6/4/107 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/devices.txt5
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/admin-guide/devices.txt b/Documentation/admin-guide/devices.txt
index 6b71852dadc2..4ec843123cc3 100644
--- a/Documentation/admin-guide/devices.txt
+++ b/Documentation/admin-guide/devices.txt
@@ -3081,3 +3081,8 @@
1 = /dev/osd1 Second OSD Device
...
255 = /dev/osd255 256th OSD Device
+
+ 384-511 char RESERVED FOR DYNAMIC ASSIGNMENT
+ Character devices that request a dynamic allocation of major
+ number will take numbers starting from 511 and downward,
+ once the 234-254 range is full.