Re: SEEK_HOLE defined but useless on linux-3.4+/ext4 [Re: small ascii files can be sparse

[Jim Meyering]

Paul Eggert wrote:
> On 07/31/2012 09:52 AM, Jim Meyering wrote:
>> fstat uses a file descriptor.
>> Calling fstatfs on that same file descriptor should
>> give a reliable (race-free) file system type.
>
> Ah, sorry, I thought the idea was to cache the
> statfs info so that we didn't need to invoke
> two system calls for each file.  But yes, if
> there's no cache we should be OK.

Using cached st_dev -> FS-type(is-compressing-FS) information is critical.
Can you outline how a grep -r X A B C might go astray due to such a
cache entry becoming stale, assuming we clear the cache between command
line arguments?

While processing each argument, I see no risk that the device associated
with our open directory FDs will be remounted on a different device with
a different class of file system.