Hi Al, Can you please take another look? Thanks, Jose On Mon, Nov 7, 2016 at 5:51 AM, Nikolaus Rath <Nikolaus@xxxxxxxx> wrote: > On Nov 03 2016, Nikolaus Rath <Nikolaus-BTH8mxji4b0@xxxxxxxxxxxxxxxx> wrote: >> On Nov 03 2016, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: >>> On Wed, Nov 02, 2016 at 11:53:40PM +0100, Jose Lopes wrote: >>>> Syscall 'ftruncate' makes the 'file' struct available to filesystem >>>> handlers. This makes it possible, e.g., for filesystems, such as, >>>> FUSE, to access the file handle associated with the file descriptor >>>> that was passed to 'ftruncate'. In the specific case of FUSE, this >>>> also makes it possible for (userspace) FUSE-based filesystems to >>>> distinguish between calls to 'truncate' and 'ftruncate'. >>> >>> Why FUSE is such a precious snowflake that it needs to make that distinction, >>> unlike all other filesystems? >> >> FUSE filesystems are often used as an extra layer on top of another >> filesystem (that stores the actual data). If the user opens a file (in >> the fuse filesystem), deletes it, and then truncates it, FUSE currently >> cannot do the same operation in the underlying filesystem: it receives >> a truncate() call with the inode, but there is no syscall that allows >> truncation for an inode. If FUSE had access to the file handle, it can >> use that to store a file descriptor for the file on the underlying >> filesystem and use ftruncate. > > In case it wasn't clear: for the case of ftruncate, fuse *does* have > access to the file handle so the problem does not arise. For the case of > fchmod, this is currently a problem (and the patch we're discussing > would fix it). > > Best, > -Nikolaus > > -- > GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599F > Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F > > »Time flies like an arrow, fruit flies like a Banana.« -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
