On 09/19/2011 12:27 PM, Sunil Mushran wrote:

On 09/19/2011 10:57 AM, Eric Blake wrote:

quoted

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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org    +1-801-349-2682
Libvirt virtualization library http://libvirt.org
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