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SubjectRe: [patch] `cp /dev/zero /tmp' (patch against 2.2.9)
Hi,

On Mon, 21 Jun 1999 13:33:21 +0200 (CEST), Andrea Arcangeli
<andrea@suse.de> said:

> I agree that currently fdatasync is just an alias for fsync. But the
> manpage seems a bit different:

> The manpage says "the metadata such as" so I thought we could skip all the
> metadata (the inode timestamp looked as an example to me). I thought it
> would be the application that should know if the last operations changed
> the metadata or not.

No. Check the Single Unix glossary:

synchronised I/O data integrity completion

For read, when the operation has been completed or diagnosed
if unsuccessful. The read is complete only when an image of
the data has been successfully transferred to the requesting
process. If there were any pending write requests affecting
the data to be read at the time that the synchronised read
operation was requested, these write requests shall be
successfully transferred prior to reading the data.

For write, when the operation has been completed or
diagnosed if unsuccessful. The write is complete only when
the data specified in the write request is successfully
transferred and all file system information required to
retrieve the data is successfully transferred.

File attributes that are not necessary for data retrieval (access
time, modification time, status change time) need not be
successfully transferred prior to returning to the calling
process.

synchronised I/O file integrity completion

Identical to a synchronised I/O data integrity completion with the
addition that all file attributes relative to the I/O operation
(including access time, modification time, status change time)
will be successfully transferred prior to returning to the calling
process.

O_DSYNC and fdatasync() can skip some of the inode updates, but when
extending the file or allocating data we need to sync the inode and the
indirect blocks too.

--Stephen

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