On Mon, Dec 16, 2024 at 11:14 PM Bernd Schubert <bschubert@xxxxxxx> wrote: > > Our file system has a translation capability for S3-to-posix. > The current value of 1kiB is enough to cover S3 keys, but > does not allow encoding of %xx escape characters. > The limit is increased to (PATH_MAX - 1), as we need > 3 x 1024 and that is close to PATH_MAX (4kB) already. > -1 is used as the terminating null is not included in the > length calculation. > > Testing large file names was hard with libfuse/example file systems, > so I created a new memfs that does not have a 255 file name length > limitation. > https://github.com/libfuse/libfuse/pull/1077 > > The connection is initialized with FUSE_NAME_LOW_MAX, which > is set to the previous value of FUSE_NAME_MAX of 1024. With > FUSE_MIN_READ_BUFFER of 8192 that is enough for two file names > + fuse headers. > When FUSE_INIT reply sets max_pages to a value > 1 we know > that fuse daemon supports request buffers of at least 2 pages > (+ header) and can therefore hold 2 x PATH_MAX file names - operations > like rename or link that need two file names are no issue then. > > Signed-off-by: Bernd Schubert <bschubert@xxxxxxx> > --- > fs/fuse/dev.c | 4 ++-- > fs/fuse/dir.c | 2 +- > fs/fuse/fuse_i.h | 11 +++++++++-- > fs/fuse/inode.c | 8 ++++++++ > 4 files changed, 20 insertions(+), 5 deletions(-) > > diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c > index c979ce93685f8338301a094ac513c607f44ba572..3b4bdff84e534be8b1ce4a970e841b6a362ef176 100644 > --- a/fs/fuse/dev.c > +++ b/fs/fuse/dev.c > @@ -1538,7 +1538,7 @@ static int fuse_notify_inval_entry(struct fuse_conn *fc, unsigned int size, > goto err; > > err = -ENAMETOOLONG; > - if (outarg.namelen > FUSE_NAME_MAX) > + if (outarg.namelen > fc->name_max) > goto err; > > err = -EINVAL; > @@ -1587,7 +1587,7 @@ static int fuse_notify_delete(struct fuse_conn *fc, unsigned int size, > goto err; > > err = -ENAMETOOLONG; > - if (outarg.namelen > FUSE_NAME_MAX) > + if (outarg.namelen > fc->name_max) > goto err; > > err = -EINVAL; > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c > index 494ac372ace07ab4ea06c13a404ecc1d2ccb4f23..42db112e052f0c26d1ba9973b033b1c7cd822359 100644 > --- a/fs/fuse/dir.c > +++ b/fs/fuse/dir.c > @@ -371,7 +371,7 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name > > *inode = NULL; > err = -ENAMETOOLONG; > - if (name->len > FUSE_NAME_MAX) > + if (name->len > fm->fc->name_max) > goto out; > > > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index 74744c6f286003251564d1235f4d2ca8654d661b..5ce19bc6871291eeaa4c4af4ea935d4de80e8a00 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -38,8 +38,12 @@ > /** Bias for fi->writectr, meaning new writepages must not be sent */ > #define FUSE_NOWRITE INT_MIN > > -/** It could be as large as PATH_MAX, but would that have any uses? */ > -#define FUSE_NAME_MAX 1024 > +/** Maximum length of a filename, not including terminating null */ > + > +/* maximum, small enough for FUSE_MIN_READ_BUFFER*/ > +#define FUSE_NAME_LOW_MAX 1024 > +/* maximum, but needs a request buffer > FUSE_MIN_READ_BUFFER */ > +#define FUSE_NAME_MAX (PATH_MAX - 1) > > /** Number of dentries for each connection in the control filesystem */ > #define FUSE_CTL_NUM_DENTRIES 5 > @@ -893,6 +897,9 @@ struct fuse_conn { > /** Version counter for evict inode */ > atomic64_t evict_ctr; > > + /* maximum file name length */ > + u32 name_max; > + > /** Called on final put */ > void (*release)(struct fuse_conn *); > > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c > index 3ce4f4e81d09e867c3a7db7b1dbb819f88ed34ef..4d61dacedf6a1684eb5dc39a6f56ded0ca4c1fe4 100644 > --- a/fs/fuse/inode.c > +++ b/fs/fuse/inode.c > @@ -978,6 +978,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm, > fc->user_ns = get_user_ns(user_ns); > fc->max_pages = FUSE_DEFAULT_MAX_PAGES_PER_REQ; > fc->max_pages_limit = fuse_max_pages_limit; > + fc->name_max = FUSE_NAME_LOW_MAX; > > if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH)) > fuse_backing_files_init(fc); > @@ -1335,6 +1336,13 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args, > fc->max_pages = > min_t(unsigned int, fc->max_pages_limit, > max_t(unsigned int, arg->max_pages, 1)); > + > + /* > + * PATH_MAX file names might need two pages for > + * ops like rename > + */ > + if (fc->max_pages > 1) > + fc->name_max = FUSE_NAME_MAX; For the case of FUSE_REANME (and FUSE_RENAME2, FUSE_SYMLINK) with large file-names (4095) you would need 3 pages (PAGE_SIZE=4096): fuse_in_header (40) + fuse_rename_in (8) + names (2 * 4095). > } > if (IS_ENABLED(CONFIG_FUSE_DAX)) { > if (flags & FUSE_MAP_ALIGNMENT && > > -- > 2.43.0 >
