On Thu, 2007-03-08 at 23:39 +0100, Ihar `Philips` Filipau wrote: > The problem have beaten me before. And now I have it again. > Imaging external hard drive with "proper" file system (proper == > supports posix permissions) where files were created by user A and > then it (ext. hard drive) was brought to another location/computer and > user B tried to read them. Failure. Why? Because Linux preserved > permissions on hard drive - though they are already irrelevant on > system fs is currently mounted on. And that renders literally all > files accessible only by root. > > What is needed is special mount option to tell file system (*): > (1) to ignore permissions when file/directory is read; > (2) when file/directory is created it receives automatically "world > writable" permissions 0666 (I cannot imaging how to simulate "user > friendly" file attribute "read-only", though it seems not relevant to > external storage anyway). > > I'm looking into the code and it seems that every file system parses > option on their own. > Global flags (ro/rw, nodev, etc) are handled by mount(8) itself and > passed to sys_mount() as bitmask. > > How gid/uid are passed to file system? I do not see them in > parameter list to sys_mount(). Or they are handled somehow otherwise? A posix file system doesn't have a uid or gid associated with it. These are set based on the owner of the process creating the file or directory. > Any ideas on how I can simulate such behavior and or on how to > implement such attribute would be appreciated. jfs does support mount options to override uid, gid, and umask for existing files. The reason for this is so a file system can be shared between linux and os2, and os2 doesn't use these fields. (I just realized that I've never documented these flags.) I don't know how other file systems' maintainers would feel about supporting these flags. I can see how it would be useful for external hard drives. > P.S. chmod/chown isn't option since (1) they do not work for ro file > system and (2) doing that every time on NNNk files might quite > tiresome - every time disk is reattached. This is true of chown, but if you would chmod everything to 777 (or 666 for non-directories), you wouldn't have to repeat that every time you reattach. You could mount the drive under a directory with restricted permissions to have some degree of security. > P.P.S. BTW MacOSX has such option and it is automatically selected for > external hard drives. What are the details? If something were to be proposed, it wouldn't hurt to try to be consistent. > P.P.P.S. That doesn't happen with most external hard drives since they > are all FAT32. I moved to ext2/hfs+ in part to avoid the recurring > nightmares of past when I have worked with FAT32 all day long. And > also ext2/hfs+ (under Linux/MacOSX) are better than FAT*. And also I > need "case sensitiveness". Shaggy -- David Kleikamp IBM Linux Technology Center - 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
