On 12/18/24 10:15, Shachar Sharon wrote: > 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). Sure, but if you look into functions like fuse_perform_write() and fuse_direct_io(), fc->max_pages does not account the header. Maybe not documented as that, but effectively used as "payload" pages, which is also what the file/dir names are. Thanks, Bernd
