On 26/08/05 10:29PM, Darrick J. Wong wrote: > On Mon, Aug 03, 2026 at 02:29:47AM +0000, John Groves wrote: > > From: John Groves <[email protected]> > > > > Famfs file maps (fmaps) may reference multiple daxdevs. Before passing > > an fmap that references a new daxdev, the daxdev is pushed into the > > kernel via FAMFSIOC_DAXDEV_OPEN). This adds daxdevs to daxdev_table for > > index-based resolution from famfs extents to daxdevs. > > > > Signed-off-by: John Groves <[email protected]> > > --- > > fs/famfs/famfs_file.c | 74 ++++++++++++++++++++++++++++++++ > > include/uapi/linux/famfs_ioctl.h | 24 +++++++++++ > > 2 files changed, 98 insertions(+) > > > > diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c > > index e7f271ce6d03..e11a55ecf8d7 100644 > > --- a/fs/famfs/famfs_file.c > > +++ b/fs/famfs/famfs_file.c > > @@ -287,6 +287,76 @@ famfs_file_init_dax(struct file *file, void __user > > *arg) > > return rc; > > } > > > > +/** > > + * famfs_daxdev_open() - FAMFSIOC_DAXDEV_OPEN ioctl handler > > + * @file: any file in the famfs mount (the table is per-superblock) > > + * @arg: ptr to struct famfs_ioc_daxdev in user space > > + * > > + * Register a devdax device (identified by path) into the mount's daxdev > > table > > + * at the caller-specified index, so files whose extents reference that > > index > > + * can be mapped. The path is resolved by lookup_daxdev() - the same > > helper the > > + * mount uses for the primary daxdev - so every slot is resolved > > identically. > > + * Registering exposes raw device memory, so it requires CAP_SYS_RAWIO. > > + */ > > +static int > > +famfs_daxdev_open(struct file *file, void __user *arg) > > +{ > > + struct super_block *sb = file_inode(file)->i_sb; > > + struct famfs_fs_info *fsi = sb->s_fs_info; > > + struct famfs_ioc_daxdev dd; > > + dev_t devno; > > + char *path; > > + int rc; > > + > > + if (!capable(CAP_SYS_RAWIO)) > > + return -EPERM; > > + > > + if (copy_from_user(&dd, arg, sizeof(dd))) > > + return -EFAULT; > > + > > + /* @flags is reserved; reject non-zero so it stays available */ > > + if (dd.flags) > > + return -EINVAL; > > + > > + /* > > + * If this daxdev index is already populated there is nothing to do. > > + * The index is cluster-invariant, so a valid slot already names this > > + * device; skip the path resolution entirely. install_daxdev() rechecks > > + * ->valid under the write lock, so this is purely an optimization. > > + */ > > + scoped_guard(rwsem_read, &fsi->devlist_sem) { > > + if (dd.daxdev_index >= fsi->dax_devlist->nslots) > > + return -EINVAL; > > + if (fsi->dax_devlist->devlist[dd.daxdev_index].valid) > > + return 0; > > + } > > + > > + if (dd.daxdev_path_len == 0 || dd.daxdev_path_len >= PATH_MAX) > > + return -EINVAL; > > + > > + /* +1 so the terminating NUL is included within the bound */ > > + path = strndup_user((const char __user *)(uintptr_t)dd.daxdev_path, > > + dd.daxdev_path_len + 1); > > + if (IS_ERR(path)) > > + return PTR_ERR(path); > > + > > + rc = lookup_daxdev(path, &devno); > > + if (rc) > > + goto out; > > + > > + /* > > + * The daxdev table is allocated at mount time (for the slot-0 primary), > > + * so it is always present here; no need to allocate it. > > + */ > > + rc = famfs_install_daxdev(fsi, sb, dd.daxdev_index, devno, path); > > + if (rc) > > + pr_debug("%s: failed to install daxdev index %llu (%s)\n", > > + __func__, dd.daxdev_index, path); > > +out: > > + kfree(path); > > + return rc; > > +} > > + > > /** > > * famfs_file_ioctl() - Top-level famfs file ioctl handler > > * @file: the file > > @@ -308,6 +378,10 @@ famfs_file_ioctl(struct file *file, unsigned int cmd, > > unsigned long arg) > > rc = 0; > > break; > > > > + case FAMFSIOC_DAXDEV_OPEN: > > + rc = famfs_daxdev_open(file, (void __user *)arg); > > + break; > > + > > case FAMFSIOC_MAP_CREATE: > > rc = famfs_file_init_dax(file, (void __user *)arg); > > break; > > diff --git a/include/uapi/linux/famfs_ioctl.h > > b/include/uapi/linux/famfs_ioctl.h > > index b4eb373c1ade..751d8b033c2e 100644 > > --- a/include/uapi/linux/famfs_ioctl.h > > +++ b/include/uapi/linux/famfs_ioctl.h > > @@ -77,6 +77,29 @@ struct famfs_ioc_fmap_header { > > __u64 reserved1; > > }; > > > > +/** > > + * struct famfs_ioc_daxdev - register an additional backing daxdev by path > > + * @daxdev_index: the (cluster-invariant) index this daxdev occupies in > > + * extent dev_index fields. Index 0 is the mount-time > > primary. > > + * @daxdev_path: userspace pointer to the devdax device path (e.g. > > + * "/dev/dax0.0"); resolved in the kernel the same way > > the > > + * mount primary is. > > + * @daxdev_path_len: length of the path string, not counting the NUL. > > + * @flags: reserved; must be zero. > > + * > > + * Standalone famfs registers every daxdev by path: the mount primary > > comes in > > + * as the mount device name, and slots 1..n come in here. (This > > deliberately > > + * differs from fuse's fd-based FUSE_DEV_IOC_DAXDEV_OPEN; each side is > > uniform > > + * within itself.) Passing the path by pointer keeps the struct > > fixed-size, so > > + * longer paths never require an ABI change. > > + */ > > +struct famfs_ioc_daxdev { > > + __u64 daxdev_index; > > + __u64 daxdev_path; > > + __u32 daxdev_path_len; > > Can't we just pass an open fd to a dax device and have it use that > rather than doing its own path operations? > > --D
Could do, but then there would be two ways to "open" a daxdev, since the primary is passed by path via the mount command or call. If anybody thinks that's superior enough to do it 2 different ways, let me know. Otherwise I'll leave it. Thanks! John <snip>
