Re: tar does not support partial reads

[Paul Eggert]

On 7/19/21 7:54 AM, Christian Schoenebeck wrote:
> POSIX compliant applications must always expect that read() /
> write() functions might read/write less bytes than requested

Although that's true in general, it's not true for regular files. The 
POSIX spec for 'read' 
<https://pubs.opengroup.org/onlinepubs/9699919799/functions/pread.html> 
says, "The value returned may be less than /nbyte/ if the number of 
bytes left in the file is less than /nbyte/, if the /read/() request was 
interrupted by a signal, or if the file is a pipe or FIFO or special 
file and has fewer than /nbyte/ bytes immediately available for reading."

So, regular files shouldn't get short reads unless there's an EOF or a 
signal.

Perhaps someone could hack on GNU Tar to make it more robust in the 
presence of filesystems that fail to conform to POSIX. Regardless of 
that, though, your filesystem should get fixed, as lots of programs 
other than GNU Tar assume POSIX semantics for regular files.