On 2012-02-03, at 10:03 AM, Al Viro wrote: > On Fri, Feb 03, 2012 at 01:25:26AM -0700, Andreas Dilger wrote: >> On 2012-02-02, at 2:24 PM, Al Viro wrote: >>> FWIW, there's something we really should've done a long time ago: putting >>> that limit into sb->s_max_links. With 0 meaning "leave all checks to >>> ->link/->mkdir/->rename". Something like the following would make a >>> reasonable start - just the conversion of obvious cases. As the next >>> step I'd probably initialize it as ~0U instead of 0 and let the filesystems >>> that want something trickier (reiserfs, ext4, gfs2, ocfs2) explicitly set >>> it to 0 in their foo_fill_super(). That would take care of a bunch of cases >>> where we forgot to do those checks (ubifs, hfsplus, jffs2, ramfs, etc.) and >>> it's probably a saner default anyway. >> >> This would also give userspace some hope of pathconf(path, _PC_LINK_MAX) >> returning the actual value from the filesystem, instead of hard-coding >> this into glibc itself based on the statfs-returned f_type magic value. > > *snort* > > Even skipping the standard flame about pathconf() as an API, this will > not work. > * we have filesystems that do not allow link creation at all and > do keep track of subdirectories count in i_nlink of directories. What > would you have them store? As it is, ~0U works just fine, but pathconf() > users won't be happy with it. > * we have filesystems that allow unlimited subdirectories, while > limiting the number of links to non-directories; ->s_max_links == 0 will > work just fine, but won't make pathconf() happy. > * we have filesystems that have more complex rules re links to > non-directory (see mail from Chris in this thread). What would you have > pathconf() do? No comment on how good an API pathconf() is, but getting a per-filesystem value from the kernel has to be better than a hard-coded value coded in a library in userspace. Cheers, Andreas -- 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
