Messages in this thread | | | Date | Tue, 22 Sep 2015 15:25:27 -0400 | From | Theodore Ts'o <> | Subject | Re: [RFC PATCH 1/2] VFS: Kill use of O_LARGEFILE inside the kernel |
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On Tue, Sep 22, 2015 at 05:12:42PM +0100, David Howells wrote: > > Further, path-based truncate() makes no checks based on file-largeness, unlike > ftruncate().
Right, but truncate in general is used to make files *smaller* so I'm having trouble thinking of a scenario where a largefile-oblivious program could get in trouble by truncating a file > 2TB to some hard-coded length (normally zero).
> Overlayfs and one or two other places need to potentially apply O_LARGEFILE to > the things that they do on behalf of userspace - but other than suppressing > some size checks, it seems to be ignored by the filesystems and the VM.
The size checks really were the primary points of O_LARGEFILE. As I recall the primary system calls where this really matters is open(2) and stat(2) (since if st_size is too small to represent the size of the file, then the user space program could get really confused).
Essentially O_LARGEFILE is an assertion that userspace can handle handle 64-bit files, and won't get confused by system call interfaces where off_t is 32-bit wide, because it will use the 64-bit variants. So it's not at all surprising that the file systems and the VM in general doesn't need to worry about the flag.
- Ted
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