Messages in this thread | | | Date | Mon, 19 Sep 2011 12:44:07 -0600 | From | Eric Blake <> | Subject | Re: Man page doc for SEEK_DATA/SEEK_HOLE |
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On 09/19/2011 12:27 PM, Sunil Mushran wrote: > On 09/19/2011 10:57 AM, Eric Blake wrote: >> Also, it seems a shame that the kernel can fail with EINVAL instead of >> properly emulating SEEK_HOLE and SEEK_DATA even on file systems with >> no underlying support for reporting holes. >> > > Why do you say that? If I am reading generic_file_llseek_unlocked() > correctly, the default behavior is treat offset < i_size as data.
The proposed wording states:
> .B EINVAL > .I whence > -is not one of > -.BR SEEK_SET , > -.BR SEEK_CUR , > -.BR SEEK_END ; > -or the resulting file offset would be negative, > +is not valid (this error may be returned if > +.I whence > +is > +.BR SEEK_DATA > +or > +.BR SEEK_HOLE > +and the underlying file system does not support the operation).
I guess it should instead read:
EINVAL whence is not valid (this error may be returned if whence is SEEK_DATA or SEEK_HOLE but the kernel does not support the operation).
Given your argument that new enough kernels understand SEEK_DATA and SEEK_HOLE for all file systems.
I agree that EINVAL will occur if you compile against new enough glibc that exposes the constants, but then run against an older kernel that does not yet understand them. But I want the text to be clarified to be bullet-proof that if I am running against kernel 3.1 or newer, the only way I will ever get EINVAL for these two constants is if I do something else invalid, like a negative offset.
-- Eric Blake eblake@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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