On Fri, 23 Feb 2007, Dan Mick wrote:
So, that would be an "error", and, other than reporting it accurately, what
would you want ZFS to do to "support" it?
It's not an error for write(2) to return with less bytes written than
requested. In some situations, that's pretty much expected. Like, for
example, an writing to network sockets. But filesystems may also decide to
do short writes, e.g. in the case when the write would extend the file,
but the filesystem runs out of space before all of the write completed;
it's up to the implementation whether it returns ENOSPC for all of the
write or whether it returns the number of bytes successfully written. Same
if you exceed the rlimits or quota allocations; if the write is
interrupted before completion.
dudekula mastan wrote:
If a write call attempted to write X bytes of data, and if writecall writes
only x ( hwere x <X) bytes, then we call that write as short write.
-Masthan
> Please let me know the ZFS support for short writes ?
In the sense that it does them ? Well, it's UNIX/POSIX standard to do
them, the write(2) manpage puts it like this:
If a write() requests that more bytes be written than there
is room for-for example, if the write would exceed the pro-
cess file size limit (see getrlimit(2) and ulimit(2)), the
system file size limit, or the free space on the device-only
as many bytes as there is room for will be written. For
example, suppose there is space for 20 bytes more in a file
before reaching a limit. A write() of 512-bytes returns 20.
The next write() of a non-zero number of bytes gives a
failure return (except as noted for pipes and FIFO below).
I.e. you get a partial write before a failing write. ZFS behaves like
this (on quota, definitely - "filesystem full" on ZFS is a bit different
due to the space needs for COW), just as other filesystems do.
Where have you encountered a filesystem _NOT_ supporting this behaviour ?
FrankH.
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