Architecture - Open by fid - Revision history

Docadmin at 21:19, 22 January 2010

2010-01-22T21:19:17Z

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	'''''Note:''''' The content on this page reflects the state of design of a Lustre feature at a particular point in time and may contain outdated information.		'''''Note:''''' ''The content on this page reflects the state of design of a Lustre feature at a particular point in time and may contain outdated information.''

	== Purpose ==		== Purpose ==

Docadmin: Protected "Architecture - Open by fid" ([edit=sysop] (indefinite) [move=sysop] (indefinite))

2010-01-22T21:19:07Z

Protected "Architecture - Open by fid" ([edit=sysop] (indefinite) [move=sysop] (indefinite))

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2010-01-19T00:19:33Z

Purpose

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			'''''Note:''''' The content on this page reflects the state of design of a Lustre feature at a particular point in time and may contain outdated information.

	== Purpose ==		== Purpose ==

Docadmin: moved Architecture - QAS open by fid to Architecture - Open by fid

2010-01-14T23:56:49Z

moved Architecture - QAS open by fid to Architecture - Open by fid

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2010-01-14T23:56:35Z

Docadmin: moved QAS open by fid to Architecture - QAS open by fid

2010-01-14T21:09:46Z

moved QAS open by fid to Architecture - QAS open by fid

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Docadmin: 1 revision

2010-01-14T21:01:06Z

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Adilger at 17:21, 24 July 2007

2007-07-24T17:21:36Z

New page

== Purpose ==

Open by fid returns a file descriptor based on a FID. This is quite similar to the controversial open by inode calls found elsewhere.

== Implementation Choices ==

There several considerations for implementation:
# use an ioctl on the root directory of the lustre file system - advantage: simple implementation
# open the file /proc/fs/lustre/.../open_by_fid/FID - major advantage: this is a standard open call, so it can be used by unmodified utilities
# an easy to use, in kernel API is also required

== Decomposition of the design ==

The architecture of open by fid decomposes into several pieces:
# a local mechanism to generate a file descriptor from a ficticious pathname in /proc and/or through an ioctl
# the rpc mechanisms with the MDS to get that file descriptor (based on existing re-open by fid code, used during recovery)
# a mechanism to set flags and default flags on fid file descriptors
# verification and implementation of the recovery of the file descriptor during an MDS failure
# verification and implementation of correct behavior when file descriptor calls are made
## IO using the file descriptor: this can be dependent on flags, e.g. IO may or may not trigger cache miss handling
## fstat, fchown, ftruncate etc.

== Use cases to cover ==

{|cellspacing="0" border="1"
!Description
!Semantics
|-
|deployment|| open by fid is done on Lustre client nodes
|-
|open a fid residing the mds||file handle for file io
|-
|open a fid residing on oss||file handle for object io
|-
|open /proc/fs/lustre/something/FID|| returns synthetic file descriptor for the object
|-
|open /proc/fs/lustre/something/FID_FLAGS|| returns synthetic file descriptor for the object and sets flags on the file descriptor, for example to avoid cache misses
|-
|open_by_fid()||ioctl with the same functionality as opening the /proc file.
|-
|authorization||servers allow open_by_fid() only from certain nodes
|-
|mount options||clients do not enable open by fid unless a mount option is passed, clients can set the default flags to be used when open by fid file descriptors are generated.
|-
|Failure modes || the open calls should be subject to replay / resend, including the restoration of flags on the server
|}

== Category ==
[[Category:QAS|Open by FID]]
[[Category:Architecture|Open by FID]]

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	\|Failure modes \|\| the open calls should be subject to replay / resend, including the restoration of flags on the server		\|Failure modes \|\| the open calls should be subject to replay / resend, including the restoration of flags on the server
	\|}		\|}


	~~== Category ==~~
	~~[[Category:QAS\|Open by FID]]~~
	~~[[Category:Architecture\|Open by FID]]~~