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IDProjectCategoryView StatusDate SubmittedLast Update
0002533OCamlOCaml generalpublic2004-04-30 17:002013-08-30 23:27
Reporteradministrator 
Assigned Toshinwell 
PrioritynormalSeverityfeatureReproducibilityalways
StatusassignedResolutionopen 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version 
Summary0002533: Feature wish: Unix.fsync, etc.
DescriptionHi,

having to write a very filesystem-oriented system, I am in need of system
calls for synchronizing the in-core state of files and directories with
that on disk.

It would be nice to see the following easily implementable system calls
in the Unix-module (currently I'm working with extensions):

  val fsync : file_descr -> unit
  val fdatasync : file_descr -> unit
  val dirfd : dir_handle -> file_descr

The last function (BSD, the other two are POSIX.1b) is needed, because
synchronizing data with fdatasync (and also metadata + data with fsync)
does not synchronize the directory entries as such. For this it is
necessary to extract the file descriptor from the directory stream and
explicitly call fsync on it.

If there are reasons not to exhibit the file_descr associated with a
dir_handle, a function "val dir_sync : dir_handle -> unit" would also
be a possibility.

It may be too inefficient to open files with every write being
synchronized (O_SYNC, etc.). Sometimes I even only want the directory
to be synchronized, not the data.

Best regards,
Markus

--
Markus Mottl http://www.oefai.at/~markus [^] markus@oefai.at

Tagspatch
Attached Files

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-  Notes
(0005252)
mottl (reporter)
2010-02-25 19:24

This has been around for a really long time. I think at least the following POSIX system calls concerning syncing should be supported: sync and fsync. They are available on virtually every Unix system and indispensable for applications that need persistence guarantees.

Note that fdatasync is not supported on FreeBSD and Mac OS X.
(0005270)
avsm (reporter)
2010-03-20 21:19

fsync(2) is also more relaxed on MacOS X; it needs the F_FULLFSYNC fcntl to ensure it actually hits the disk in-order.
(0005277)
shinwell (developer)
2010-03-30 13:01

Markus, do you have a pre-existing patch for this (or could you construct one) which could be looked at?
(0005281)
mottl (reporter)
2010-03-30 16:21

Yes, just take a look at our Core-library, file "unix_ext_stubs.c". It contains a function "unix_fsync" that can surely be taken verbatim.

There are several other functions there that could probably be added to the OCaml distribution immediately, because they are well-standardized in POSIX and do not require elaborate API additions (types, etc.). E.g. pselect, abort, sync.

Some of the others are also well-standardized, but would need extra types, etc. I'm not sure what the OCaml team's preferred procedure for adding those would be.

- Issue History
Date Modified Username Field Change
2005-11-18 10:13 administrator New Issue
2010-02-25 19:24 mottl Note Added: 0005252
2010-03-20 21:19 avsm Note Added: 0005270
2010-03-30 13:01 shinwell Note Added: 0005277
2010-03-30 13:02 shinwell Status acknowledged => assigned
2010-03-30 13:02 shinwell Assigned To => shinwell
2010-03-30 16:21 mottl Note Added: 0005281
2013-08-30 23:27 doligez Tag Attached: patch


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