302f0493f0
Describe use of jiffy-based timeout values involved in inode maintenance. Signed-off-by: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Martin Brandenburg <martin@omnibond.com>
448 lines
17 KiB
Text
448 lines
17 KiB
Text
ORANGEFS
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========
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OrangeFS is an LGPL userspace scale-out parallel storage system. It is ideal
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for large storage problems faced by HPC, BigData, Streaming Video,
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Genomics, Bioinformatics.
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Orangefs, originally called PVFS, was first developed in 1993 by
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Walt Ligon and Eric Blumer as a parallel file system for Parallel
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Virtual Machine (PVM) as part of a NASA grant to study the I/O patterns
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of parallel programs.
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Orangefs features include:
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* Distributes file data among multiple file servers
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* Supports simultaneous access by multiple clients
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* Stores file data and metadata on servers using local file system
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and access methods
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* Userspace implementation is easy to install and maintain
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* Direct MPI support
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* Stateless
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MAILING LIST
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============
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http://beowulf-underground.org/mailman/listinfo/pvfs2-users
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DOCUMENTATION
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=============
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http://www.orangefs.org/documentation/
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USERSPACE FILESYSTEM SOURCE
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===========================
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http://www.orangefs.org/download
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Orangefs versions prior to 2.9.3 would not be compatible with the
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upstream version of the kernel client.
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BUILDING THE USERSPACE FILESYSTEM ON A SINGLE SERVER
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====================================================
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When Orangefs is upstream, "--with-kernel" shouldn't be needed, but
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until then the path to where the kernel with the Orangefs kernel client
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patch was built is needed to ensure that pvfs2-client-core (the bridge
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between kernel space and user space) will build properly. You can omit
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--prefix if you don't care that things are sprinkled around in
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/usr/local.
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./configure --prefix=/opt/ofs --with-kernel=/path/to/orangefs/kernel
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make
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make install
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Create an orangefs config file:
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/opt/ofs/bin/pvfs2-genconfig /etc/pvfs2.conf
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for "Enter hostnames", use the hostname, don't let it default to
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localhost.
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create a pvfs2tab file in /etc:
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cat /etc/pvfs2tab
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tcp://myhostname:3334/orangefs /mymountpoint pvfs2 defaults,noauto 0 0
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create the mount point you specified in the tab file if needed:
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mkdir /mymountpoint
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bootstrap the server:
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/opt/ofs/sbin/pvfs2-server /etc/pvfs2.conf -f
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start the server:
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/opt/osf/sbin/pvfs2-server /etc/pvfs2.conf
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Now the server is running. At this point you might like to
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prove things are working with:
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/opt/osf/bin/pvfs2-ls /mymountpoint
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You might not want to enforce selinux, it doesn't seem to matter by
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linux 3.11...
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If stuff seems to be working, turn on the client core:
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/opt/osf/sbin/pvfs2-client -p /opt/osf/sbin/pvfs2-client-core
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Mount your filesystem.
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mount -t pvfs2 tcp://myhostname:3334/orangefs /mymountpoint
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OPTIONS
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=======
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The following mount options are accepted:
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acl
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Allow the use of Access Control Lists on files and directories.
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intr
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Some operations between the kernel client and the user space
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filesystem can be interruptible, such as changes in debug levels
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and the setting of tunable parameters.
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local_lock
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Enable posix locking from the perspective of "this" kernel. The
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default file_operations lock action is to return ENOSYS. Posix
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locking kicks in if the filesystem is mounted with -o local_lock.
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Distributed locking is being worked on for the future.
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DEBUGGING
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=========
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If you want the debug (GOSSIP) statements in a particular
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source file (inode.c for example) go to syslog:
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echo inode > /sys/kernel/debug/orangefs/kernel-debug
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No debugging (the default):
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echo none > /sys/kernel/debug/orangefs/kernel-debug
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Debugging from several source files:
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echo inode,dir > /sys/kernel/debug/orangefs/kernel-debug
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All debugging:
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echo all > /sys/kernel/debug/orangefs/kernel-debug
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Get a list of all debugging keywords:
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cat /sys/kernel/debug/orangefs/debug-help
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PROTOCOL BETWEEN KERNEL MODULE AND USERSPACE
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============================================
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Orangefs is a user space filesystem and an associated kernel module.
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We'll just refer to the user space part of Orangefs as "userspace"
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from here on out. Orangefs descends from PVFS, and userspace code
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still uses PVFS for function and variable names. Userspace typedefs
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many of the important structures. Function and variable names in
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the kernel module have been transitioned to "orangefs", and The Linux
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Coding Style avoids typedefs, so kernel module structures that
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correspond to userspace structures are not typedefed.
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The kernel module implements a pseudo device that userspace
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can read from and write to. Userspace can also manipulate the
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kernel module through the pseudo device with ioctl.
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THE BUFMAP:
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At startup userspace allocates two page-size-aligned (posix_memalign)
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mlocked memory buffers, one is used for IO and one is used for readdir
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operations. The IO buffer is 41943040 bytes and the readdir buffer is
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4194304 bytes. Each buffer contains logical chunks, or partitions, and
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a pointer to each buffer is added to its own PVFS_dev_map_desc structure
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which also describes its total size, as well as the size and number of
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the partitions.
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A pointer to the IO buffer's PVFS_dev_map_desc structure is sent to a
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mapping routine in the kernel module with an ioctl. The structure is
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copied from user space to kernel space with copy_from_user and is used
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to initialize the kernel module's "bufmap" (struct orangefs_bufmap), which
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then contains:
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* refcnt - a reference counter
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* desc_size - PVFS2_BUFMAP_DEFAULT_DESC_SIZE (4194304) - the IO buffer's
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partition size, which represents the filesystem's block size and
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is used for s_blocksize in super blocks.
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* desc_count - PVFS2_BUFMAP_DEFAULT_DESC_COUNT (10) - the number of
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partitions in the IO buffer.
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* desc_shift - log2(desc_size), used for s_blocksize_bits in super blocks.
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* total_size - the total size of the IO buffer.
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* page_count - the number of 4096 byte pages in the IO buffer.
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* page_array - a pointer to page_count * (sizeof(struct page*)) bytes
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of kcalloced memory. This memory is used as an array of pointers
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to each of the pages in the IO buffer through a call to get_user_pages.
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* desc_array - a pointer to desc_count * (sizeof(struct orangefs_bufmap_desc))
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bytes of kcalloced memory. This memory is further intialized:
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user_desc is the kernel's copy of the IO buffer's ORANGEFS_dev_map_desc
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structure. user_desc->ptr points to the IO buffer.
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pages_per_desc = bufmap->desc_size / PAGE_SIZE
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offset = 0
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bufmap->desc_array[0].page_array = &bufmap->page_array[offset]
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bufmap->desc_array[0].array_count = pages_per_desc = 1024
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bufmap->desc_array[0].uaddr = (user_desc->ptr) + (0 * 1024 * 4096)
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offset += 1024
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.
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.
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.
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bufmap->desc_array[9].page_array = &bufmap->page_array[offset]
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bufmap->desc_array[9].array_count = pages_per_desc = 1024
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bufmap->desc_array[9].uaddr = (user_desc->ptr) +
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(9 * 1024 * 4096)
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offset += 1024
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* buffer_index_array - a desc_count sized array of ints, used to
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indicate which of the IO buffer's partitions are available to use.
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* buffer_index_lock - a spinlock to protect buffer_index_array during update.
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* readdir_index_array - a five (ORANGEFS_READDIR_DEFAULT_DESC_COUNT) element
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int array used to indicate which of the readdir buffer's partitions are
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available to use.
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* readdir_index_lock - a spinlock to protect readdir_index_array during
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update.
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OPERATIONS:
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The kernel module builds an "op" (struct orangefs_kernel_op_s) when it
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needs to communicate with userspace. Part of the op contains the "upcall"
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which expresses the request to userspace. Part of the op eventually
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contains the "downcall" which expresses the results of the request.
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The slab allocator is used to keep a cache of op structures handy.
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At init time the kernel module defines and initializes a request list
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and an in_progress hash table to keep track of all the ops that are
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in flight at any given time.
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Ops are stateful:
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* unknown - op was just initialized
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* waiting - op is on request_list (upward bound)
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* inprogr - op is in progress (waiting for downcall)
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* serviced - op has matching downcall; ok
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* purged - op has to start a timer since client-core
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exited uncleanly before servicing op
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* given up - submitter has given up waiting for it
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When some arbitrary userspace program needs to perform a
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filesystem operation on Orangefs (readdir, I/O, create, whatever)
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an op structure is initialized and tagged with a distinguishing ID
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number. The upcall part of the op is filled out, and the op is
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passed to the "service_operation" function.
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Service_operation changes the op's state to "waiting", puts
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it on the request list, and signals the Orangefs file_operations.poll
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function through a wait queue. Userspace is polling the pseudo-device
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and thus becomes aware of the upcall request that needs to be read.
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When the Orangefs file_operations.read function is triggered, the
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request list is searched for an op that seems ready-to-process.
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The op is removed from the request list. The tag from the op and
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the filled-out upcall struct are copy_to_user'ed back to userspace.
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If any of these (and some additional protocol) copy_to_users fail,
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the op's state is set to "waiting" and the op is added back to
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the request list. Otherwise, the op's state is changed to "in progress",
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and the op is hashed on its tag and put onto the end of a list in the
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in_progress hash table at the index the tag hashed to.
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When userspace has assembled the response to the upcall, it
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writes the response, which includes the distinguishing tag, back to
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the pseudo device in a series of io_vecs. This triggers the Orangefs
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file_operations.write_iter function to find the op with the associated
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tag and remove it from the in_progress hash table. As long as the op's
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state is not "canceled" or "given up", its state is set to "serviced".
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The file_operations.write_iter function returns to the waiting vfs,
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and back to service_operation through wait_for_matching_downcall.
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Service operation returns to its caller with the op's downcall
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part (the response to the upcall) filled out.
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The "client-core" is the bridge between the kernel module and
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userspace. The client-core is a daemon. The client-core has an
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associated watchdog daemon. If the client-core is ever signaled
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to die, the watchdog daemon restarts the client-core. Even though
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the client-core is restarted "right away", there is a period of
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time during such an event that the client-core is dead. A dead client-core
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can't be triggered by the Orangefs file_operations.poll function.
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Ops that pass through service_operation during a "dead spell" can timeout
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on the wait queue and one attempt is made to recycle them. Obviously,
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if the client-core stays dead too long, the arbitrary userspace processes
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trying to use Orangefs will be negatively affected. Waiting ops
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that can't be serviced will be removed from the request list and
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have their states set to "given up". In-progress ops that can't
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be serviced will be removed from the in_progress hash table and
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have their states set to "given up".
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Readdir and I/O ops are atypical with respect to their payloads.
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- readdir ops use the smaller of the two pre-allocated pre-partitioned
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memory buffers. The readdir buffer is only available to userspace.
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The kernel module obtains an index to a free partition before launching
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a readdir op. Userspace deposits the results into the indexed partition
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and then writes them to back to the pvfs device.
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- io (read and write) ops use the larger of the two pre-allocated
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pre-partitioned memory buffers. The IO buffer is accessible from
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both userspace and the kernel module. The kernel module obtains an
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index to a free partition before launching an io op. The kernel module
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deposits write data into the indexed partition, to be consumed
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directly by userspace. Userspace deposits the results of read
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requests into the indexed partition, to be consumed directly
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by the kernel module.
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Responses to kernel requests are all packaged in pvfs2_downcall_t
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structs. Besides a few other members, pvfs2_downcall_t contains a
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union of structs, each of which is associated with a particular
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response type.
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The several members outside of the union are:
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- int32_t type - type of operation.
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- int32_t status - return code for the operation.
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- int64_t trailer_size - 0 unless readdir operation.
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- char *trailer_buf - initialized to NULL, used during readdir operations.
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The appropriate member inside the union is filled out for any
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particular response.
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PVFS2_VFS_OP_FILE_IO
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fill a pvfs2_io_response_t
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PVFS2_VFS_OP_LOOKUP
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fill a PVFS_object_kref
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PVFS2_VFS_OP_CREATE
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fill a PVFS_object_kref
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PVFS2_VFS_OP_SYMLINK
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fill a PVFS_object_kref
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PVFS2_VFS_OP_GETATTR
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fill in a PVFS_sys_attr_s (tons of stuff the kernel doesn't need)
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fill in a string with the link target when the object is a symlink.
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PVFS2_VFS_OP_MKDIR
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fill a PVFS_object_kref
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PVFS2_VFS_OP_STATFS
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fill a pvfs2_statfs_response_t with useless info <g>. It is hard for
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us to know, in a timely fashion, these statistics about our
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distributed network filesystem.
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PVFS2_VFS_OP_FS_MOUNT
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fill a pvfs2_fs_mount_response_t which is just like a PVFS_object_kref
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except its members are in a different order and "__pad1" is replaced
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with "id".
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PVFS2_VFS_OP_GETXATTR
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fill a pvfs2_getxattr_response_t
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PVFS2_VFS_OP_LISTXATTR
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fill a pvfs2_listxattr_response_t
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PVFS2_VFS_OP_PARAM
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fill a pvfs2_param_response_t
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PVFS2_VFS_OP_PERF_COUNT
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fill a pvfs2_perf_count_response_t
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PVFS2_VFS_OP_FSKEY
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file a pvfs2_fs_key_response_t
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PVFS2_VFS_OP_READDIR
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jamb everything needed to represent a pvfs2_readdir_response_t into
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the readdir buffer descriptor specified in the upcall.
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Userspace uses writev() on /dev/pvfs2-req to pass responses to the requests
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made by the kernel side.
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A buffer_list containing:
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- a pointer to the prepared response to the request from the
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kernel (struct pvfs2_downcall_t).
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- and also, in the case of a readdir request, a pointer to a
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buffer containing descriptors for the objects in the target
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directory.
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... is sent to the function (PINT_dev_write_list) which performs
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the writev.
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PINT_dev_write_list has a local iovec array: struct iovec io_array[10];
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The first four elements of io_array are initialized like this for all
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responses:
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io_array[0].iov_base = address of local variable "proto_ver" (int32_t)
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io_array[0].iov_len = sizeof(int32_t)
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io_array[1].iov_base = address of global variable "pdev_magic" (int32_t)
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io_array[1].iov_len = sizeof(int32_t)
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io_array[2].iov_base = address of parameter "tag" (PVFS_id_gen_t)
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io_array[2].iov_len = sizeof(int64_t)
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io_array[3].iov_base = address of out_downcall member (pvfs2_downcall_t)
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of global variable vfs_request (vfs_request_t)
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io_array[3].iov_len = sizeof(pvfs2_downcall_t)
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Readdir responses initialize the fifth element io_array like this:
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io_array[4].iov_base = contents of member trailer_buf (char *)
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from out_downcall member of global variable
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vfs_request
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io_array[4].iov_len = contents of member trailer_size (PVFS_size)
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from out_downcall member of global variable
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vfs_request
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Orangefs exploits the dcache in order to avoid sending redundant
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requests to userspace. We keep object inode attributes up-to-date with
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orangefs_inode_getattr. Orangefs_inode_getattr uses two arguments to
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help it decide whether or not to update an inode: "new" and "bypass".
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Orangefs keeps private data in an object's inode that includes a short
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timeout value, getattr_time, which allows any iteration of
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orangefs_inode_getattr to know how long it has been since the inode was
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updated. When the object is not new (new == 0) and the bypass flag is not
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set (bypass == 0) orangefs_inode_getattr returns without updating the inode
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if getattr_time has not timed out. Getattr_time is updated each time the
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inode is updated.
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Creation of a new object (file, dir, sym-link) includes the evaluation of
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its pathname, resulting in a negative directory entry for the object.
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A new inode is allocated and associated with the dentry, turning it from
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a negative dentry into a "productive full member of society". Orangefs
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obtains the new inode from Linux with new_inode() and associates
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the inode with the dentry by sending the pair back to Linux with
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d_instantiate().
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The evaluation of a pathname for an object resolves to its corresponding
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dentry. If there is no corresponding dentry, one is created for it in
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the dcache. Whenever a dentry is modified or verified Orangefs stores a
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short timeout value in the dentry's d_time, and the dentry will be trusted
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for that amount of time. Orangefs is a network filesystem, and objects
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can potentially change out-of-band with any particular Orangefs kernel module
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instance, so trusting a dentry is risky. The alternative to trusting
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dentries is to always obtain the needed information from userspace - at
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least a trip to the client-core, maybe to the servers. Obtaining information
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from a dentry is cheap, obtaining it from userspace is relatively expensive,
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hence the motivation to use the dentry when possible.
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The timeout values d_time and getattr_time are jiffy based, and the
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code is designed to avoid the jiffy-wrap problem:
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"In general, if the clock may have wrapped around more than once, there
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is no way to tell how much time has elapsed. However, if the times t1
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and t2 are known to be fairly close, we can reliably compute the
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difference in a way that takes into account the possibility that the
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clock may have wrapped between times."
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from course notes by instructor Andy Wang
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