Le 11/06/2013 23:04, Mark Fasheh a écrit : > On Tue, Jun 11, 2013 at 10:56:59PM +0200, Gabriel de Perthuis wrote: >>> What I found however is that neither of these is a great idea ;) >>> >>> - We want to require that the inode be open for writing so that an >>> unprivileged user can't do things like run dedupe on a performance >>> sensitive file that they might only have read access to. In addition I >>> could see it as kind of a surprise (non-standard behavior) to an >>> administrator that users could alter the layout of files they are only >>> allowed to read. >>> >>> - Readonly snapshots won't let you open for write anyway (unsuprisingly, >>> open() returns -EROFS). So that kind of kills the idea of them being able >>> to open those files for write which we want to dedupe. >>> >>> That said, I still think being able to run this against a set of readonly >>> snapshots makes sense especially if those snapshots are taken for backup >>> purposes. I'm just not sure how we can sanely enable it. >> >> The check could be: if (fmode_write || cap_sys_admin). >> >> This isn't incompatible with mnt_want_write, that check is at the >> level of the superblocks and vfsmount and not the subvolume fsid. > > Oh ok that's certainly better. I think we still have a problem though - how > does a process gets write access to a file from a ro-snapshot? If I open a > file (as root) on a ro-snapshot on my test machine here I'll get -EROFS.
Your first series did work in that case. The process does get a read-only fd, but that's no obstacle for the ioctl. > I'm a bit confused - how does mnt_want_write factor in here? I think that's > for a totally seperate kind of accounting, right? It doesn't, it's just that I had spent a few minutes checking anyway. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
