[S390] dasd: allocate fallback cqr for reserve/release
The DASD reserve and release ioctls use the preallocated memory pool of the respective device to build their CCW requests. However, when the device is busy, the pool may already be empty and the ioctl fails. Usually this can be recovered by calling the ioctl again, but in a situation in which we need to issue an unconditional reserve to make a device operational again, this would be not recoverable. To avoid a failure due to lack of memory, DASD device driver will preallocate enough memory for a single reserve/release request, which can be used if normal allocation fails. Signed-off-by: NStefan Weinhuber <wein@de.ibm.com> Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
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