Hi, Sorry for the long delay Darrick.
> > + fextent.fe_logical = 0;
> > + fextent.fe_physical = 0;
> > + fieinfo.fi_extents_max = 1;
> > + fieinfo.fi_extents_mapped = 0;
> > + fieinfo.fi_extents_start = &fextent;
> > + fieinfo.fi_start = start;
> > + fieinfo.fi_len = 1 << inode->i_blkbits;
> > + fieinfo.fi_flags = 0;
> > + fieinfo.fi_cb = fiemap_fill_kernel_extent;
> > +
> > + error = inode->i_op->fiemap(inode, &fieinfo);
> > +
> > + if (error)
> > + return error;
> > +
> > + if (fieinfo.fi_flags & (FIEMAP_EXTENT_UNKNOWN |
> > + FIEMAP_EXTENT_ENCODED |
> > + FIEMAP_EXTENT_DATA_INLINE |
> > + FIEMAP_EXTENT_UNWRITTEN))
> > + return -EINVAL;
>
> AFAICT, three of the filesystems that support COW writes (xfs, ocfs2,
> and btrfs) do not return bmap results for files with shared blocks.
> This check here should include FIEMAP_EXTENT_SHARED since external
> overwrites of a COW file block are bad news on btrfs (and ocfs2 and
> xfs).
ok, np
>
> > +
> > + *block = (fextent.fe_physical +
> > + (start - fextent.fe_logical)) >> inode->i_blkbits;
>
> Hmmm, so there's nothing here checking that the physical device fiemap
> reports is the same device that was passed into the mount. This is
> trivially true for most of the filesystems that implement bmap and
> fiemap, but definitely not true for xfs or btrfs. I would bet most
> userspace callers of bmap (since it's an ext2-era ioctl) make that
> assumption and don't even know how to find the device.
Makes sense.
>
> On xfs, the bmap implementation won't return any results for realtime
> files, but it looks as though we suddenly will start doing that here,
> because in the new bmap implementation we will use fiemap, and fiemap
> reports extents without providing any context about which device they're
> on, and that context-less extent gets passed back to bmap_fiemap.
>
> In any case, I think a better solution to the multi-device problem is to
> start returning device information via struct fiemap_extent, at least
> inside the kernel. Use one of the reserved fields to declare a new
> '__u32 fe_device' field in struct fiemap_extent which can be the dev_t
> device number, and then you can check that against inode->i_sb->s_bdev
> to avoid returning results for the non-primary device of a multi-device
> filesystem.
I agree we should address it here, but I don't think fiemap_extent is the right
place for it, it is linked to the UAPI, and changing it is usually not a good
idea.
I think I got your idea anyway, but, what if, instead returning the bdev in
fiemap_extent, we instead, send a flag (via fi_flags) to the filesystem, to
idenfify a FIBMAP or a FIEMAP call, and let the filesystem decide what to do
with such information?
>
> > +
> > + return error;
> > +}
> > +
> > /**
> > * bmap - find a block number in a file
> > * @inode: inode owning the block number being requested
> > @@ -1594,10 +1628,14 @@ EXPORT_SYMBOL(iput);
> > */
> > int bmap(struct inode *inode, sector_t *block)
> > {
> > - if (!inode->i_mapping->a_ops->bmap)
> > + if (inode->i_op->fiemap)
> > + return bmap_fiemap(inode, block);
> > + else if (inode->i_mapping->a_ops->bmap)
> > + *block = inode->i_mapping->a_ops->bmap(inode->i_mapping,
> > + *block);
> > + else
> > return -EINVAL;
>
> Waitaminute. btrfs currently supports fiemap but not bmap, and now
> suddenly it will support this legacy interface they've never supported
> before. Are they on board with this?
>
> --D
>
> >
> > - *block = inode->i_mapping->a_ops->bmap(inode->i_mapping, *block);
> > return 0;
> > }
> > EXPORT_SYMBOL(bmap);
> > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > index 6086978fe01e..bfa59df332bf 100644
> > --- a/fs/ioctl.c
> > +++ b/fs/ioctl.c
> > @@ -116,6 +116,38 @@ int fiemap_fill_user_extent(struct fiemap_extent_info *fieinfo, u64 logical,
> > return (flags & FIEMAP_EXTENT_LAST) ? 1 : 0;
> > }
> >
> > +int fiemap_fill_kernel_extent(struct fiemap_extent_info *fieinfo, u64 logical,
> > + u64 phys, u64 len, u32 flags)
> > +{
> > + struct fiemap_extent *extent = fieinfo->fi_extents_start;
> > +
> > + /* only count the extents */
> > + if (fieinfo->fi_extents_max == 0) {
> > + fieinfo->fi_extents_mapped++;
> > + return (flags & FIEMAP_EXTENT_LAST) ? 1 : 0;
> > + }
> > +
> > + if (fieinfo->fi_extents_mapped >= fieinfo->fi_extents_max)
> > + return 1;
> > +
> > + if (flags & SET_UNKNOWN_FLAGS)
> > + flags |= FIEMAP_EXTENT_UNKNOWN;
> > + if (flags & SET_NO_UNMOUNTED_IO_FLAGS)
> > + flags |= FIEMAP_EXTENT_ENCODED;
> > + if (flags & SET_NOT_ALIGNED_FLAGS)
> > + flags |= FIEMAP_EXTENT_NOT_ALIGNED;
> > +
> > + extent->fe_logical = logical;
> > + extent->fe_physical = phys;
> > + extent->fe_length = len;
> > + extent->fe_flags = flags;
> > +
> > + fieinfo->fi_extents_mapped++;
> > +
> > + if (fieinfo->fi_extents_mapped == fieinfo->fi_extents_max)
> > + return 1;
> > + return (flags & FIEMAP_EXTENT_LAST) ? 1 : 0;
> > +}
> > /**
> > * fiemap_fill_next_extent - Fiemap helper function
> > * @fieinfo: Fiemap context passed into ->fiemap
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 7a434979201c..28bb523d532a 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1711,6 +1711,8 @@ struct fiemap_extent_info {
> > fiemap_fill_cb fi_cb;
> > };
> >
> > +int fiemap_fill_kernel_extent(struct fiemap_extent_info *info, u64 logical,
> > + u64 phys, u64 len, u32 flags);
> > int fiemap_fill_next_extent(struct fiemap_extent_info *info, u64 logical,
> > u64 phys, u64 len, u32 flags);
> > int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags);
> > --
> > 2.17.2
> >
--
Carlos
