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2008-10-09block: add blk_rq_aligned helper functionFUJITA Tomonori
This adds blk_rq_aligned helper function to see if alignment and padding requirement is satisfied for DMA transfer. This also converts blk_rq_map_kern and __blk_rq_map_user to use the helper function. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Cc: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: introduce struct rq_map_data to use reserved pagesFUJITA Tomonori
This patch introduces struct rq_map_data to enable bio_copy_use_iov() use reserved pages. Currently, bio_copy_user_iov allocates bounce pages but drivers/scsi/sg.c wants to allocate pages by itself and use them. struct rq_map_data can be used to pass allocated pages to bio_copy_user_iov. The current users of bio_copy_user_iov simply passes NULL (they don't want to use pre-allocated pages). Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Cc: Jens Axboe <jens.axboe@oracle.com> Cc: Douglas Gilbert <dougg@torque.net> Cc: Mike Christie <michaelc@cs.wisc.edu> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: add gfp_mask argument to blk_rq_map_user and blk_rq_map_user_iovFUJITA Tomonori
Currently, blk_rq_map_user and blk_rq_map_user_iov always do GFP_KERNEL allocation. This adds gfp_mask argument to blk_rq_map_user and blk_rq_map_user_iov so sg can use it (sg always does GFP_ATOMIC allocation). Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Signed-off-by: Douglas Gilbert <dougg@torque.net> Cc: Mike Christie <michaelc@cs.wisc.edu> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09cfq-iosched: fix queue depth detectionAaron Carroll
CFQ's detection of queueing devices assumes a non-queuing device and detects if the queue depth reaches a certain threshold. Under some workloads (e.g. synchronous reads), CFQ effectively forces a unit queue depth, thus defeating the detection logic. This leads to poor performance on queuing hardware, since the idle window remains enabled. This patch inverts the sense of the logic: assume a queuing-capable device, and detect if the depth does not exceed the threshold. Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: don't use bio_has_data() in the completion pathJens Axboe
We should just check for rq->bio, as that is really the information we are looking for. Even if the bio attached doesn't carry data, we still need to do IO post processing on it. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: inherit CPU completion on bio->rq and rq->rq mergesJens Axboe
Somewhat incomplete, as we do allow merges of requests and bios that have different completion CPUs given. This is done on the assumption that a larger IO is still more beneficial than CPU locality. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: add support for IO CPU affinityJens Axboe
This patch adds support for controlling the IO completion CPU of either all requests on a queue, or on a per-request basis. We export a sysfs variable (rq_affinity) which, if set, migrates completions of requests to the CPU that originally submitted it. A bio helper (bio_set_completion_cpu()) is also added, so that queuers can ask for completion on that specific CPU. In testing, this has been show to cut the system time by as much as 20-40% on synthetic workloads where CPU affinity is desired. This requires a little help from the architecture, so it'll only work as designed for archs that are using the new generic smp helper infrastructure. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: make kblockd_schedule_work() take the queue as parameterJens Axboe
Preparatory patch for checking queuing affinity. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: split softirq handling into blk-softirq.cJens Axboe
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: use linux/uaccess.h in elevator.c instead of asm variantJens Axboe
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: allow disk to have extended device numberTejun Heo
Now that disk and partition handlings are mostly unified, it's easy to allow disk to have extended device number. This patch makes add_disk() use extended device number if disk->minors is zero. Both sd and ide-disk are updated to use this. * sd_format_disk_name() is implemented which can generically determine the drive name. This removes disk number restriction stemming from limited device names. * If sd index goes over SD_MAX_DISKS (which can be increased now BTW), sd simply doesn't initialize minors letting block layer choose extended device number. * If CONFIG_DEBUG_EXT_DEVT is set, both sd and ide-disk always set minors to 0 and use extended device numbers. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: replace @ext_minors with GENHD_FL_EXT_DEVTTejun Heo
With previous changes, it's meaningless to limit the number of partitions. Replace @ext_minors with GENHD_FL_EXT_DEVT such that setting the flag allows the disk to have maximum number of allowed partitions (only limited by the number of entries in parsed_partitions as determined by MAX_PART constant). This kills not-too-pretty alloc_disk_ext[_node]() functions and makes @minors parameter to alloc_disk[_node]() unnecessary. The parameter is left alone to avoid disturbing the users. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: make partition array dynamicTejun Heo
disk->__part used to be statically allocated to the maximum possible number of partitions. This patch makes partition array allocation dynamic. The added overhead is minimal as only real change is one memory dereference changed to RCU one. This saves both a bit of memory and cpu cycles iterating through unoccupied slots and makes increasing partition limit easier. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: move stats from disk to part0Tejun Heo
Move stats related fields - stamp, in_flight, dkstats - from disk to part0 and unify stat handling such that... * part_stat_*() now updates part0 together if the specified partition is not part0. ie. part_stat_*() are now essentially all_stat_*(). * {disk|all}_stat_*() are gone. * part_round_stats() is updated similary. It handles part0 stats automatically and disk_round_stats() is killed. * part_{inc|dec}_in_fligh() is implemented which automatically updates part0 stats for parts other than part0. * disk_map_sector_rcu() is updated to return part0 if no part matches. Combined with the above changes, this makes NULL special case handling in callers unnecessary. * Separate stats show code paths for disk are collapsed into part stats show code paths. * Rename disk_stat_lock/unlock() to part_stat_lock/unlock() While at it, reposition stat handling macros a bit and add missing parentheses around macro parameters. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: kill GENHD_FL_FAIL and use part0->make_it_failTejun Heo
GENHD_FL_FAIL for disk is what make_it_fail is for parts. Kill it and use part0->make_it_fail. Sysfs node handling is unified too. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: always set bdev->bd_partTejun Heo
Till now, bdev->bd_part is set only if the bdev was for parts other than part0. This patch makes bdev->bd_part always set so that code paths don't have to differenciate common handling. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: move holder_dir from disk to part0Tejun Heo
Move disk->holder_dir to part0->holder_dir. Kill now mostly superflous bdev_get_holder(). While at it, kill superflous kobject_get/put() around holder_dir, slave_dir and cmd_filter creation and collapse disk_sysfs_add_subdirs() into register_disk(). These serve no purpose but obfuscating the code. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: move policy from disk to part0Tejun Heo
Move disk->policy to part0->policy. Implement and use get_disk_ro(). Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: unify sysfs size node handlingTejun Heo
Now that capacity and __dev are moved to part0, part0 and others can share the same method. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: move __dev from disk to part0Tejun Heo
Move disk->__dev to part0->__dev. This simplifies bdget_disk() and lookup_devt() and allows common sysfs attributes to be unified. part_to_disk() is updated to handle part0 -> disk. Updated to include a fix from Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>, he writes: "part0 is a "special" partition and doesn't need to have capacity set - this fixes regression caused by "block: move __dev from disk to part0" commit." Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: introduce partition 0Tejun Heo
genhd and partition code handled disk and partitions separately. All information about the whole disk was in struct genhd and partitions in struct hd_struct. However, the whole disk (part0) and other partitions have a lot in common and the data structures end up having good number of common fields and thus separate code paths doing the same thing. Also, the partition array was indexed by partno - 1 which gets pretty confusing at times. This patch introduces partition 0 and makes the partition array indexed by partno. Following patches will unify the handling of disk and parts piece-by-piece. This patch also implements disk_partitionable() which tests whether a disk is partitionable. With coming dynamic partition array change, the most common usage of disk_max_parts() will be testing whether a disk is partitionable and the number of max partitions will become much less important. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: implement and use {disk|part}_to_dev()Tejun Heo
Implement {disk|part}_to_dev() and use them to access generic device instead of directly dereferencing {disk|part}->dev. To make sure no user is left behind, rename generic devices fields to __dev. This is in preparation of unifying partition 0 handling with other partitions. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: implement CONFIG_DEBUG_BLOCK_EXT_DEVTTejun Heo
Extended devt introduces non-contiguos device numbers. This patch implements a debug option which forces most devt allocations to be from the extended area and spreads them out. This is enabled by default if DEBUG_KERNEL is set and achieves... 1. Detects code paths in kernel or userland which expect predetermined consecutive device numbers. 2. When something goes wrong, avoid corruption as adding to the minor of earlier partition won't lead to the wrong but valid device. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: adjust formatting for large minors and add ext_range sysfs attrTejun Heo
With extended minors and the soon-to-follow debug feature, large minor numbers for block devices will be common. This patch does the followings to make printouts pretty. * Adapt print formats such that large minors don't break the formatting. * For extended MAJ:MIN, %02x%02x for MAJ:MIN used in printk_all_partitions() doesn't cut it anymore. Update it such that %03x:%05x is used if either MAJ or MIN doesn't fit in %02x. * Implement ext_range sysfs attribute which shows total minors the device can use including both conventional minor space and the extended one. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: implement extended dev numbersTejun Heo
Implement extended device numbers. A block driver can tell block layer that it wants to use extended device numbers. After the usual minor space is used up, block layer automatically allocates devt's from EXT_BLOCK_MAJOR. Currently only one major number is allocated for this but as the allocation is strictly on-demand, ~1mil minor space under it should suffice unless the system actually has more than ~1mil partitions and if that ever happens adding more majors to the extended devt area is easy. Due to internal implementation issues, the first partition can't be allocated on the extended area. In other words, genhd->minors should at least be 1. This limitation will be lifted by later changes. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: fix diskstats accessTejun Heo
There are two variants of stat functions - ones prefixed with double underbars which don't care about preemption and ones without which disable preemption before manipulating per-cpu counters. It's unclear whether the underbarred ones assume that preemtion is disabled on entry as some callers don't do that. This patch unifies diskstats access by implementing disk_stat_lock() and disk_stat_unlock() which take care of both RCU (for partition access) and preemption (for per-cpu counter access). diskstats access should always be enclosed between the two functions. As such, there's no need for the versions which disables preemption. They're removed and double underbars ones are renamed to drop the underbars. As an extra argument is added, there's no danger of using the old version unconverted. disk_stat_lock() uses get_cpu() and returns the cpu index and all diskstat functions which access per-cpu counters now has @cpu argument to help RT. This change adds RCU or preemption operations at some places but also collapses several preemption ops into one at others. Overall, the performance difference should be negligible as all involved ops are very lightweight per-cpu ones. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: fix disk->part[] dereferencing raceTejun Heo
disk->part[] is protected by its matching bdev's lock. However, non-critical accesses like collecting stats and printing out sysfs and proc information used to be performed without any locking. As partitions can come and go dynamically, partitions can go away underneath those non-critical accesses. As some of those accesses are writes, this theoretically can lead to silent corruption. This patch fixes the race by using RCU for the partition array and dev reference counter to hold partitions. * Rename disk->part[] to disk->__part[] to make sure no one outside genhd layer proper accesses it directly. * Use RCU for disk->__part[] dereferencing. * Implement disk_{get|put}_part() which can be used to get and put partitions from gendisk respectively. * Iterators are implemented to help iterate through all partitions safely. * Functions which require RCU readlock are marked with _rcu suffix. * Use disk_put_part() in __blkdev_put() instead of directly putting the contained kobject. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: don't depend on consecutive minor spaceTejun Heo
* Implement disk_devt() and part_devt() and use them to directly access devt instead of computing it from ->major and ->first_minor. Note that all references to ->major and ->first_minor outside of block layer is used to determine devt of the disk (the part0) and as ->major and ->first_minor will continue to represent devt for the disk, converting these users aren't strictly necessary. However, convert them for consistency. * Implement disk_max_parts() to avoid directly deferencing genhd->minors. * Update bdget_disk() such that it doesn't assume consecutive minor space. * Move devt computation from register_disk() to add_disk() and make it the only one (all other usages use the initially determined value). These changes clean up the code and will help disk->part dereference fix and extended block device numbers. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: make variable and argument names more consistentTejun Heo
In hd_struct, @partno is used to denote partition number and a number of other places use @part to denote hd_struct. Functions use @part and @index instead. This causes confusion and makes it difficult to use consistent variable names for hd_struct. Always use @partno if a variable represents partition number. Also, print out functions use @f or @part for seq_file argument. Use @seqf uniformly instead. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: misc updatesTejun Heo
This patch makes the following misc updates in preparation for disk->part dereference fix and extended block devt support. * implment part_to_disk() * fix comment about gendisk->part indexing * rename get_part() to disk_map_sector() * don't use n which is always zero while printing disk information in diskstats_show() Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: update add_partition() error handlingTejun Heo
d805dda4 tried to fix error case handling in add_partition() but had a few problems. * disk->part[] entry is set early and left dangling if operation fails. * Once device initialized, the last put_device() is responsible for freeing all the resources. The failure path freed part_stats and p regardless of put_device() causing double free. * holders subdir holds reference to the disk device, so failure path should remove it to release resources properly which was missing. This patch fixes the above problems and while at it move partition slot busy check into add_partition() for completeness and inlines holders subdirectory creation. Using separate function for it just obfuscates the code. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Abdel Benamrouche <draconux@gmail.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: allow deleting zero length partitionTejun Heo
delete_partition() was noop for zero length partition. As the addition code allows creating zero lenght partition and deletion is assumed to always succeed, this causes memory leak for zero length partitions. Allow zero length partitions to end their meaningless lives. While at it, allow deleting zero lenght partition via BLKPG_DEL_PARTITION ioctl too. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: use class_dev_iterator instead of class_for_each_device()Tejun Heo
Recent block_class iteration updates 5c6f35c5..27f3025 converted all class device iteration to class_for_each_device() and class_find_device(), which are correct but pain in the ass to use. This pach converts them to newly introduced class_dev_iterator so that they can use more natural control structures instead of separate callbacks and struct to pass parameters to them. This results in smaller and easier code. This patch also restores the original behavior of not printing header in /proc/partitions if there's no partition to print. This is trivial but still user-visible behavior. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: don't grab block_class_lock unnecessarilyTejun Heo
block_class_lock protects major_names array and bdev_map and doesn't have anything to do with block class devices. Don't grab them while iterating over block class devices. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: fix partition info printoutsTejun Heo
Recent block_class iteration updates 5c6f35c5..27f3025 broke partition info printouts. * printk_all_partitions(): Partition print out stops when it meets a partition hole. Partition printing inner loop should continue instead of exiting on empty partition slot. * /proc/partitions and /proc/diskstats: If all information can't be read in single read(), the information is truncated. This is because find_start() doesn't actually update the counter containing the initial seek. It runs to the end and ends up always reporting EOF on the second read. This patch fixes both problems. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09Add some block/ source files to the kernel-api docbook. Fix kernel-doc ↵Randy Dunlap
notation in them as needed. Fix changed function parameter names. Fix typos/spellos. In comments, change REQ_SPECIAL to REQ_TYPE_SPECIAL and REQ_BLOCK_PC to REQ_TYPE_BLOCK_PC. Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09drop vmerge accountingMikulas Patocka
Remove hw_segments field from struct bio and struct request. Without virtual merge accounting they have no purpose. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: drop virtual merging accountingMikulas Patocka
Remove virtual merge accounting. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09deadline-iosched: non-functional fixesAaron Carroll
* convert goto to simpler while loop; * use rq_end_sector() instead of computing manually; * fix false comments; * remove spurious whitespace; * convert rq_rb_root macro to an inline function. Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09deadline-iosched: allow non-sequential batchingAaron Carroll
Deadline currently only batches sector-contiguous requests, so except for a few circumstances (e.g. requests in a single direction), it is essentially first come first served. This is bad for throughput, so change it to CSCAN, which means requests in a batch do not need to be sequential and are issued in increasing sector order. Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09Allow elevators to sort/merge discard requestsDavid Woodhouse
But blkdev_issue_discard() still emits requests which are interpreted as soft barriers, because naïve callers might otherwise issue subsequent writes to those same sectors, which might cross on the queue (if they're reallocated quickly enough). Callers still _can_ issue non-barrier discard requests, but they have to take care of queue ordering for themselves. Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09Add BLKDISCARD ioctl to allow userspace to discard sectorsDavid Woodhouse
We may well want mkfs tools to use this to mark the whole device as unwanted before they format it, for example. The ioctl takes a pair of uint64_ts, which are start offset and length in _bytes_. Although at the moment it might make sense for them both to be in 512-byte sectors, I don't want to limit the ABI to that. Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09Use WRITE_BARRIER in blkdev_issue_flush(), not (1<<BIO_RW_BARRIER)OGAWA Hirofumi
Barriers should be submitted with the WRITE flag set. Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09blktrace: simplify flags handling in __blk_add_traceDavid Woodhouse
Let the compiler see what's going on, and it can all get a lot simpler. On PPC64 this reduces the size of the code calculating these bits by about 60%. On x86_64 it's less of a win -- only 40%. Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09blktrace: support discard requestsDavid Woodhouse
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09Add 'discard' request handlingDavid Woodhouse
Some block devices benefit from a hint that they can forget the contents of certain sectors. Add basic support for this to the block core, along with a 'blkdev_issue_discard()' helper function which issues such requests. The caller doesn't get to provide an end_io functio, since blkdev_issue_discard() will automatically split the request up into multiple bios if appropriate. Neither does the function wait for completion -- it's expected that callers won't care about when, or even _if_, the request completes. It's only a hint to the device anyway. By definition, the file system doesn't _care_ about these sectors any more. [With feedback from OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> and Jens Axboe <jens.axboe@oracle.com] Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09Fix up comments about matching flags between bio and rqDavid Woodhouse
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: use bio_has_data() in the IO completion pathJens Axboe
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: use bio_has_data() to check for data carrying bioJens Axboe
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09SG_IO block filter whitelist missing MMC SET READ AHEAD commandxiphmont@xiph.org
I have another request for the block filter SG_IO command whitelist, specifically the MMC streaming command set SET READ AHEAD command. The command applies only to MMC CDROM/DVDROM drives with the streaming optional feature set. The command is useful to cdparanoia in that it allows explicit cache control side effects that are, on many drives, cdparanoia's most efficient way to flush/disable the media cache on cdrom drives. I am aware of no reason why it should not be accessible from usespace. Also note that the command is already fully accessible through the SCSI-native version of the SG_IO ioctl as well as the traditional SG interface. The command is only being refused on block devices. That means that on a typical stock distro, the command is available through /dev/sg* but not /dev/scd* although both are typically available and accessible. Filtering the command is not providing any protection, only a confusing inconsistency. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>