On 2017-03-13, Grant Edwards <[email protected]> wrote:
> After upgrading to a new version of busybox (1.25.1), I now have an
> odd problem with 'cat'. When stdout is a file, it _appears_ to be
> doing a seek to the beginning of the output file between input files.
[...]
> But, strace doesn't show any seeks. I see that 'cat' is using
> sendfile mutiple times. According to sendfile(2):
>
> In Linux kernels before 2.6.33, out_fd must refer to a socket. Since
> Linux 2.6.33 it can be any file. If it is a regular file, then send‐
> file() changes the file offset appropriately.
>
> Apparently "change file file offset apprpriatly" means it gets reset
> to zero after every call to sendfile(). I take it this implementation
> of 'cat' works for other people?
Apologies for the noise -- I finally stumbled across
CONFIG_FEATURE_USE_SENDFILE, and disabling that fixes the 'cat'
problem with 2.6.33 kernels.
--
Grant Edwards grant.b.edwards Yow! I smell a RANCID
at CORN DOG!
gmail.com
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