lix/src/libutil/immutable.cc
Eelco Dolstra b9c2b4d5b4 Remove setting of the immutable bit
Using the immutable bit is problematic, especially in conjunction with
store optimisation.  For instance, if the garbage collector deletes a
file, it has to clear its immutable bit, but if the file has
additional hard links, we can't set the bit afterwards because we
don't know the remaining paths.

So now that we support having the entire Nix store as a read-only
mount, we may as well drop the immutable bit.  Unfortunately, we have
to keep the code to clear the immutable bit for backwards
compatibility.
2012-09-19 16:17:54 -04:00

50 lines
1.2 KiB
C++

#include "config.h"
#include "immutable.hh"
#include "util.hh"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#if HAVE_LINUX_FS_H
#include <linux/fs.h>
#include <sys/ioctl.h>
#include <errno.h>
#endif
namespace nix {
void makeMutable(const Path & path)
{
#if defined(FS_IOC_SETFLAGS) && defined(FS_IOC_GETFLAGS) && defined(FS_IMMUTABLE_FL)
/* Don't even try if we're not root. One day we should support
the CAP_LINUX_IMMUTABLE capability. */
if (getuid() != 0) return;
/* The O_NOFOLLOW is important to prevent us from changing the
mutable bit on the target of a symlink (which would be a
security hole). */
AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_NOFOLLOW);
if (fd == -1) {
if (errno == ELOOP) return; // it's a symlink
throw SysError(format("opening file `%1%'") % path);
}
unsigned int flags = 0, old;
/* Silently ignore errors getting/setting the immutable flag so
that we work correctly on filesystems that don't support it. */
if (ioctl(fd, FS_IOC_GETFLAGS, &flags)) return;
old = flags;
flags &= ~FS_IMMUTABLE_FL;
if (old == flags) return;
if (ioctl(fd, FS_IOC_SETFLAGS, &flags)) return;
#endif
}
}