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@xxxxxxxxxx +1-801-349-2682
Libvirt virtualization library http://libvirt.org
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