| Message ID | 20241003234732.GB147780@ZenIV (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | introduce struct fderr, convert overlayfs uses to that | expand |
On Fri, Oct 04, 2024 at 12:47:32AM GMT, Al Viro wrote: > Similar to struct fd; unlike struct fd, it can represent > error values. > > Accessors: > > * fd_empty(f): true if f represents an error > * fd_file(f): just as for struct fd it yields a pointer to > struct file if fd_empty(f) is false. If > fd_empty(f) is true, fd_file(f) is guaranteed > _not_ to be an address of any object (IS_ERR() > will be true in that case) > * fd_err(f): if f represents an error, returns that error, > otherwise the return value is junk. > > Constructors: > > * ERR_FDERR(-E...): an instance encoding given error [ERR_FDERR, perhaps?] > * BORROWED_FDERR(file): if file points to a struct file instance, > return a struct fderr representing that file > reference with no flags set. > if file is an ERR_PTR(-E...), return a struct > fderr representing that error. > file MUST NOT be NULL. > * CLONED_FDERR(file): similar, but in case when file points to > a struct file instance, set FDPUT_FPUT in flags. > > Same destructor as for struct fd; I'm not entirely convinced that > playing with _Generic is a good idea here, but for now let's go Why? It's exactly what it's very useful for and I've used it myself this way. I think that's good use of _Generic. > that way... > > See fs/overlayfs/file.c for example of use. > > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> > --- > fs/overlayfs/file.c | 128 +++++++++++++++++++++---------------------- > include/linux/file.h | 37 +++++++++++-- > 2 files changed, 95 insertions(+), 70 deletions(-) > > diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c > index 4504493b20be..c711fa5d802f 100644 > --- a/fs/overlayfs/file.c > +++ b/fs/overlayfs/file.c > @@ -89,56 +89,46 @@ static int ovl_change_flags(struct file *file, unsigned int flags) > return 0; > } > > -static int ovl_real_fdget_meta(const struct file *file, struct fd *real, > - bool allow_meta) > +static struct fderr ovl_real_fdget_meta(const struct file *file, bool allow_meta) > { > struct dentry *dentry = file_dentry(file); > struct file *realfile = file->private_data; > struct path realpath; > int err; > > - real->word = (unsigned long)realfile; > - > if (allow_meta) { > ovl_path_real(dentry, &realpath); > } else { > /* lazy lookup and verify of lowerdata */ > err = ovl_verify_lowerdata(dentry); > if (err) > - return err; > + return ERR_FDERR(err); > > ovl_path_realdata(dentry, &realpath); > } > if (!realpath.dentry) > - return -EIO; > + return ERR_FDERR(-EIO); > > /* Has it been copied up since we'd opened it? */ > - if (unlikely(file_inode(realfile) != d_inode(realpath.dentry))) { > - struct file *f = ovl_open_realfile(file, &realpath); > - if (IS_ERR(f)) > - return PTR_ERR(f); > - real->word = (unsigned long)f | FDPUT_FPUT; > - return 0; > - } > + if (unlikely(file_inode(realfile) != d_inode(realpath.dentry))) > + return CLONED_FDERR(ovl_open_realfile(file, &realpath)); > > /* Did the flags change since open? */ > - if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS)) > - return ovl_change_flags(realfile, file->f_flags); > + if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS)) { > + err = ovl_change_flags(realfile, file->f_flags); > + if (err) > + return ERR_FDERR(err); > + } > > - return 0; > + return BORROWED_FDERR(realfile); > } > > -static int ovl_real_fdget(const struct file *file, struct fd *real) > +static struct fderr ovl_real_fdget(const struct file *file) > { > - if (d_is_dir(file_dentry(file))) { > - struct file *f = ovl_dir_real_file(file, false); > - if (IS_ERR(f)) > - return PTR_ERR(f); > - real->word = (unsigned long)f; > - return 0; > - } > + if (d_is_dir(file_dentry(file))) > + return BORROWED_FDERR(ovl_dir_real_file(file, false)); > > - return ovl_real_fdget_meta(file, real, false); > + return ovl_real_fdget_meta(file, false); > } > > static int ovl_open(struct inode *inode, struct file *file) > @@ -183,7 +173,7 @@ static int ovl_release(struct inode *inode, struct file *file) > static loff_t ovl_llseek(struct file *file, loff_t offset, int whence) > { > struct inode *inode = file_inode(file); > - struct fd real; > + struct fderr real; > const struct cred *old_cred; > loff_t ret; > > @@ -199,9 +189,9 @@ static loff_t ovl_llseek(struct file *file, loff_t offset, int whence) > return vfs_setpos(file, 0, 0); > } > > - ret = ovl_real_fdget(file, &real); > - if (ret) > - return ret; > + real = ovl_real_fdget(file); > + if (fd_empty(real)) > + return fd_err(real); > > /* > * Overlay file f_pos is the master copy that is preserved > @@ -262,7 +252,7 @@ static void ovl_file_accessed(struct file *file) > static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter) > { > struct file *file = iocb->ki_filp; > - struct fd real; > + struct fderr real; > ssize_t ret; > struct backing_file_ctx ctx = { > .cred = ovl_creds(file_inode(file)->i_sb), > @@ -273,9 +263,9 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter) > if (!iov_iter_count(iter)) > return 0; > > - ret = ovl_real_fdget(file, &real); > - if (ret) > - return ret; > + real = ovl_real_fdget(file); > + if (fd_empty(real)) > + return fd_err(real); > > ret = backing_file_read_iter(fd_file(real), iter, iocb, iocb->ki_flags, > &ctx); > @@ -288,7 +278,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter) > { > struct file *file = iocb->ki_filp; > struct inode *inode = file_inode(file); > - struct fd real; > + struct fderr real; > ssize_t ret; > int ifl = iocb->ki_flags; > struct backing_file_ctx ctx = { > @@ -304,9 +294,11 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter) > /* Update mode */ > ovl_copyattr(inode); > > - ret = ovl_real_fdget(file, &real); > - if (ret) > + real = ovl_real_fdget(file); > + if (fd_empty(real)) { > + ret = fd_err(real); > goto out_unlock; > + } > > if (!ovl_should_sync(OVL_FS(inode->i_sb))) > ifl &= ~(IOCB_DSYNC | IOCB_SYNC); > @@ -329,7 +321,7 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos, > struct pipe_inode_info *pipe, size_t len, > unsigned int flags) > { > - struct fd real; > + struct fderr real; > ssize_t ret; > struct backing_file_ctx ctx = { > .cred = ovl_creds(file_inode(in)->i_sb), > @@ -337,9 +329,9 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos, > .accessed = ovl_file_accessed, > }; > > - ret = ovl_real_fdget(in, &real); > - if (ret) > - return ret; > + real = ovl_real_fdget(in); > + if (fd_empty(real)) > + return fd_err(real); > > ret = backing_file_splice_read(fd_file(real), ppos, pipe, len, flags, &ctx); > fdput(real); > @@ -358,7 +350,7 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos, > static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, > loff_t *ppos, size_t len, unsigned int flags) > { > - struct fd real; > + struct fderr real; > struct inode *inode = file_inode(out); > ssize_t ret; > struct backing_file_ctx ctx = { > @@ -371,9 +363,11 @@ static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, > /* Update mode */ > ovl_copyattr(inode); > > - ret = ovl_real_fdget(out, &real); > - if (ret) > + real = ovl_real_fdget(out); > + if (fd_empty(real)) { > + ret = fd_err(real); > goto out_unlock; > + } > > ret = backing_file_splice_write(pipe, fd_file(real), ppos, len, flags, &ctx); > fdput(real); > @@ -386,7 +380,7 @@ static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, > > static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync) > { > - struct fd real; > + struct fderr real; > const struct cred *old_cred; > int ret; > > @@ -394,9 +388,9 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync) > if (ret <= 0) > return ret; > > - ret = ovl_real_fdget_meta(file, &real, !datasync); > - if (ret) > - return ret; > + real = ovl_real_fdget_meta(file, !datasync); > + if (fd_empty(real)) > + return fd_err(real); > > /* Don't sync lower file for fear of receiving EROFS error */ > if (file_inode(fd_file(real)) == ovl_inode_upper(file_inode(file))) { > @@ -425,7 +419,7 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma) > static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len) > { > struct inode *inode = file_inode(file); > - struct fd real; > + struct fderr real; > const struct cred *old_cred; > int ret; > > @@ -435,10 +429,11 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len > ret = file_remove_privs(file); > if (ret) > goto out_unlock; > - > - ret = ovl_real_fdget(file, &real); > - if (ret) > + real = ovl_real_fdget(file); > + if (fd_empty(real)) { > + ret = fd_err(real); > goto out_unlock; > + } > > old_cred = ovl_override_creds(file_inode(file)->i_sb); > ret = vfs_fallocate(fd_file(real), mode, offset, len); > @@ -457,13 +452,13 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len > > static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice) > { > - struct fd real; > + struct fderr real; > const struct cred *old_cred; > int ret; > > - ret = ovl_real_fdget(file, &real); > - if (ret) > - return ret; > + real = ovl_real_fdget(file); > + if (fd_empty(real)) > + return fd_err(real); > > old_cred = ovl_override_creds(file_inode(file)->i_sb); > ret = vfs_fadvise(fd_file(real), offset, len, advice); > @@ -485,7 +480,7 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in, > loff_t len, unsigned int flags, enum ovl_copyop op) > { > struct inode *inode_out = file_inode(file_out); > - struct fd real_in, real_out; > + struct fderr real_in, real_out; > const struct cred *old_cred; > loff_t ret; > > @@ -498,13 +493,16 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in, > goto out_unlock; > } > > - ret = ovl_real_fdget(file_out, &real_out); > - if (ret) > + real_out = ovl_real_fdget(file_out); > + if (fd_empty(real_out)) { > + ret = fd_err(real_out); > goto out_unlock; > + } > > - ret = ovl_real_fdget(file_in, &real_in); > - if (ret) { > + real_in = ovl_real_fdget(file_in); > + if (fd_empty(real_in)) { > fdput(real_out); > + ret = fd_err(real_in); > goto out_unlock; > } > > @@ -577,13 +575,13 @@ static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in, > > static int ovl_flush(struct file *file, fl_owner_t id) > { > - struct fd real; > + struct fderr real; > const struct cred *old_cred; > - int err; > + int err = 0; > > - err = ovl_real_fdget(file, &real); > - if (err) > - return err; > + real = ovl_real_fdget(file); > + if (fd_empty(real)) > + return fd_err(real); > > if (fd_file(real)->f_op->flush) { > old_cred = ovl_override_creds(file_inode(file)->i_sb); > diff --git a/include/linux/file.h b/include/linux/file.h > index f98de143245a..d85352523368 100644 > --- a/include/linux/file.h > +++ b/include/linux/file.h > @@ -44,13 +44,26 @@ static inline void fput_light(struct file *file, int fput_needed) > struct fd { > unsigned long word; > }; > + > +/* either a reference to struct file + flags > + * (cloned vs. borrowed, pos locked), with > + * flags stored in lower bits of value, > + * or an error (represented by small negative value). > + */ > +struct fderr { > + unsigned long word; > +}; > + > #define FDPUT_FPUT 1 > #define FDPUT_POS_UNLOCK 2 > > +#define fd_empty(f) _Generic((f), \ > + struct fd: unlikely(!(f).word), \ > + struct fderr: IS_ERR_VALUE((f).word)) > #define fd_file(f) ((struct file *)((f).word & ~(FDPUT_FPUT|FDPUT_POS_UNLOCK))) > -static inline bool fd_empty(struct fd f) > +static inline long fd_err(struct fderr f) > { > - return unlikely(!f.word); > + return (long)f.word; > } > > #define EMPTY_FD (struct fd){0} > @@ -63,11 +76,25 @@ static inline struct fd CLONED_FD(struct file *f) > return (struct fd){(unsigned long)f | FDPUT_FPUT}; > } > > -static inline void fdput(struct fd fd) > +static inline struct fderr ERR_FDERR(long n) > +{ > + return (struct fderr){(unsigned long)n}; > +} > +static inline struct fderr BORROWED_FDERR(struct file *f) > { > - if (fd.word & FDPUT_FPUT) > - fput(fd_file(fd)); > + return (struct fderr){(unsigned long)f}; > } > +static inline struct fderr CLONED_FDERR(struct file *f) > +{ > + if (IS_ERR(f)) > + return BORROWED_FDERR(f); > + return (struct fderr){(unsigned long)f | FDPUT_FPUT}; > +} > + > +#define fdput(f) (void) (_Generic((f), \ > + struct fderr: IS_ERR_VALUE((f).word), \ > + struct fd: true) && \ > + ((f).word & FDPUT_FPUT) && (fput(fd_file(f)),0)) > > extern struct file *fget(unsigned int fd); > extern struct file *fget_raw(unsigned int fd); > -- > 2.39.5 >
On Fri, Oct 4, 2024 at 1:47 AM Al Viro <viro@zeniv.linux.org.uk> wrote: > > Similar to struct fd; unlike struct fd, it can represent > error values. > > Accessors: > > * fd_empty(f): true if f represents an error > * fd_file(f): just as for struct fd it yields a pointer to > struct file if fd_empty(f) is false. If > fd_empty(f) is true, fd_file(f) is guaranteed > _not_ to be an address of any object (IS_ERR() > will be true in that case) > * fd_err(f): if f represents an error, returns that error, > otherwise the return value is junk. > > Constructors: > > * ERR_FDERR(-E...): an instance encoding given error [ERR_FDERR, perhaps?] > * BORROWED_FDERR(file): if file points to a struct file instance, > return a struct fderr representing that file > reference with no flags set. > if file is an ERR_PTR(-E...), return a struct > fderr representing that error. > file MUST NOT be NULL. > * CLONED_FDERR(file): similar, but in case when file points to > a struct file instance, set FDPUT_FPUT in flags. > > Same destructor as for struct fd; I'm not entirely convinced that > playing with _Generic is a good idea here, but for now let's go > that way... > > See fs/overlayfs/file.c for example of use. I had already posted an alternative code for overlayfs, but in case this is going to be used anyway in overlayfs or in another code, see some comments below... > > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> > --- > fs/overlayfs/file.c | 128 +++++++++++++++++++++---------------------- > include/linux/file.h | 37 +++++++++++-- > 2 files changed, 95 insertions(+), 70 deletions(-) > [...] > diff --git a/include/linux/file.h b/include/linux/file.h > index f98de143245a..d85352523368 100644 > --- a/include/linux/file.h > +++ b/include/linux/file.h > @@ -44,13 +44,26 @@ static inline void fput_light(struct file *file, int fput_needed) > struct fd { > unsigned long word; > }; > + > +/* either a reference to struct file + flags > + * (cloned vs. borrowed, pos locked), with > + * flags stored in lower bits of value, > + * or an error (represented by small negative value). > + */ > +struct fderr { > + unsigned long word; > +}; > + > #define FDPUT_FPUT 1 > #define FDPUT_POS_UNLOCK 2 > > +#define fd_empty(f) _Generic((f), \ > + struct fd: unlikely(!(f).word), \ > + struct fderr: IS_ERR_VALUE((f).word)) I suggest adding a fd_is_err(f) helper to rhyme with IS_ERR(). > #define fd_file(f) ((struct file *)((f).word & ~(FDPUT_FPUT|FDPUT_POS_UNLOCK))) > -static inline bool fd_empty(struct fd f) > +static inline long fd_err(struct fderr f) > { > - return unlikely(!f.word); > + return (long)f.word; > } > > #define EMPTY_FD (struct fd){0} > @@ -63,11 +76,25 @@ static inline struct fd CLONED_FD(struct file *f) > return (struct fd){(unsigned long)f | FDPUT_FPUT}; > } > > -static inline void fdput(struct fd fd) > +static inline struct fderr ERR_FDERR(long n) > +{ > + return (struct fderr){(unsigned long)n}; > +} > +static inline struct fderr BORROWED_FDERR(struct file *f) > { > - if (fd.word & FDPUT_FPUT) > - fput(fd_file(fd)); > + return (struct fderr){(unsigned long)f}; > } > +static inline struct fderr CLONED_FDERR(struct file *f) > +{ > + if (IS_ERR(f)) > + return BORROWED_FDERR(f); > + return (struct fderr){(unsigned long)f | FDPUT_FPUT}; > +} > + > +#define fdput(f) (void) (_Generic((f), \ > + struct fderr: IS_ERR_VALUE((f).word), \ Should that be !IS_ERR_VALUE((f).word)? > + struct fd: true) && \ > + ((f).word & FDPUT_FPUT) && (fput(fd_file(f)),0)) > or better yet #define fd_is_err(f) _Generic((f), \ struct fd: false, \ struct fderr: IS_ERR_VALUE((f).word)) #define fdput(f) (!fd_is_err(f) && ((f).word & FDPUT_FPUT) && (fput(fd_file(f)),0)) Thanks, Amir.
On Fri, Oct 04, 2024 at 12:47:09PM +0200, Amir Goldstein wrote: > I had already posted an alternative code for overlayfs, but in case this > is going to be used anyway in overlayfs or in another code, see some > comments below... As far as I can see, the current #overlayfs-next kills the case for struct fderr; we might eventually get a valid use for it, but for the time being I'm going to strip the overlayfs-related parts of that branch (obviously), fix the braino you've spotted in fdput() and archive the branch in case it's ever needed. > > +#define fd_empty(f) _Generic((f), \ > > + struct fd: unlikely(!(f).word), \ > > + struct fderr: IS_ERR_VALUE((f).word)) > > > I suggest adding a fd_is_err(f) helper to rhyme with IS_ERR(). Umm... Dropping fd_empty() for that one, you mean? > > +#define fdput(f) (void) (_Generic((f), \ > > + struct fderr: IS_ERR_VALUE((f).word), \ > > Should that be !IS_ERR_VALUE((f).word)? It should, thanks for spotting that braino. > or better yet > > #define fd_is_err(f) _Generic((f), \ > struct fd: false, \ > struct fderr: IS_ERR_VALUE((f).word)) I think that's a bad idea; too likely to spill into struct fd users, with "it's never false here" being a nasty surprise.
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index 4504493b20be..c711fa5d802f 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -89,56 +89,46 @@ static int ovl_change_flags(struct file *file, unsigned int flags) return 0; } -static int ovl_real_fdget_meta(const struct file *file, struct fd *real, - bool allow_meta) +static struct fderr ovl_real_fdget_meta(const struct file *file, bool allow_meta) { struct dentry *dentry = file_dentry(file); struct file *realfile = file->private_data; struct path realpath; int err; - real->word = (unsigned long)realfile; - if (allow_meta) { ovl_path_real(dentry, &realpath); } else { /* lazy lookup and verify of lowerdata */ err = ovl_verify_lowerdata(dentry); if (err) - return err; + return ERR_FDERR(err); ovl_path_realdata(dentry, &realpath); } if (!realpath.dentry) - return -EIO; + return ERR_FDERR(-EIO); /* Has it been copied up since we'd opened it? */ - if (unlikely(file_inode(realfile) != d_inode(realpath.dentry))) { - struct file *f = ovl_open_realfile(file, &realpath); - if (IS_ERR(f)) - return PTR_ERR(f); - real->word = (unsigned long)f | FDPUT_FPUT; - return 0; - } + if (unlikely(file_inode(realfile) != d_inode(realpath.dentry))) + return CLONED_FDERR(ovl_open_realfile(file, &realpath)); /* Did the flags change since open? */ - if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS)) - return ovl_change_flags(realfile, file->f_flags); + if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS)) { + err = ovl_change_flags(realfile, file->f_flags); + if (err) + return ERR_FDERR(err); + } - return 0; + return BORROWED_FDERR(realfile); } -static int ovl_real_fdget(const struct file *file, struct fd *real) +static struct fderr ovl_real_fdget(const struct file *file) { - if (d_is_dir(file_dentry(file))) { - struct file *f = ovl_dir_real_file(file, false); - if (IS_ERR(f)) - return PTR_ERR(f); - real->word = (unsigned long)f; - return 0; - } + if (d_is_dir(file_dentry(file))) + return BORROWED_FDERR(ovl_dir_real_file(file, false)); - return ovl_real_fdget_meta(file, real, false); + return ovl_real_fdget_meta(file, false); } static int ovl_open(struct inode *inode, struct file *file) @@ -183,7 +173,7 @@ static int ovl_release(struct inode *inode, struct file *file) static loff_t ovl_llseek(struct file *file, loff_t offset, int whence) { struct inode *inode = file_inode(file); - struct fd real; + struct fderr real; const struct cred *old_cred; loff_t ret; @@ -199,9 +189,9 @@ static loff_t ovl_llseek(struct file *file, loff_t offset, int whence) return vfs_setpos(file, 0, 0); } - ret = ovl_real_fdget(file, &real); - if (ret) - return ret; + real = ovl_real_fdget(file); + if (fd_empty(real)) + return fd_err(real); /* * Overlay file f_pos is the master copy that is preserved @@ -262,7 +252,7 @@ static void ovl_file_accessed(struct file *file) static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter) { struct file *file = iocb->ki_filp; - struct fd real; + struct fderr real; ssize_t ret; struct backing_file_ctx ctx = { .cred = ovl_creds(file_inode(file)->i_sb), @@ -273,9 +263,9 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter) if (!iov_iter_count(iter)) return 0; - ret = ovl_real_fdget(file, &real); - if (ret) - return ret; + real = ovl_real_fdget(file); + if (fd_empty(real)) + return fd_err(real); ret = backing_file_read_iter(fd_file(real), iter, iocb, iocb->ki_flags, &ctx); @@ -288,7 +278,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter) { struct file *file = iocb->ki_filp; struct inode *inode = file_inode(file); - struct fd real; + struct fderr real; ssize_t ret; int ifl = iocb->ki_flags; struct backing_file_ctx ctx = { @@ -304,9 +294,11 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter) /* Update mode */ ovl_copyattr(inode); - ret = ovl_real_fdget(file, &real); - if (ret) + real = ovl_real_fdget(file); + if (fd_empty(real)) { + ret = fd_err(real); goto out_unlock; + } if (!ovl_should_sync(OVL_FS(inode->i_sb))) ifl &= ~(IOCB_DSYNC | IOCB_SYNC); @@ -329,7 +321,7 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, unsigned int flags) { - struct fd real; + struct fderr real; ssize_t ret; struct backing_file_ctx ctx = { .cred = ovl_creds(file_inode(in)->i_sb), @@ -337,9 +329,9 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos, .accessed = ovl_file_accessed, }; - ret = ovl_real_fdget(in, &real); - if (ret) - return ret; + real = ovl_real_fdget(in); + if (fd_empty(real)) + return fd_err(real); ret = backing_file_splice_read(fd_file(real), ppos, pipe, len, flags, &ctx); fdput(real); @@ -358,7 +350,7 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos, static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, loff_t *ppos, size_t len, unsigned int flags) { - struct fd real; + struct fderr real; struct inode *inode = file_inode(out); ssize_t ret; struct backing_file_ctx ctx = { @@ -371,9 +363,11 @@ static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, /* Update mode */ ovl_copyattr(inode); - ret = ovl_real_fdget(out, &real); - if (ret) + real = ovl_real_fdget(out); + if (fd_empty(real)) { + ret = fd_err(real); goto out_unlock; + } ret = backing_file_splice_write(pipe, fd_file(real), ppos, len, flags, &ctx); fdput(real); @@ -386,7 +380,7 @@ static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync) { - struct fd real; + struct fderr real; const struct cred *old_cred; int ret; @@ -394,9 +388,9 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync) if (ret <= 0) return ret; - ret = ovl_real_fdget_meta(file, &real, !datasync); - if (ret) - return ret; + real = ovl_real_fdget_meta(file, !datasync); + if (fd_empty(real)) + return fd_err(real); /* Don't sync lower file for fear of receiving EROFS error */ if (file_inode(fd_file(real)) == ovl_inode_upper(file_inode(file))) { @@ -425,7 +419,7 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma) static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len) { struct inode *inode = file_inode(file); - struct fd real; + struct fderr real; const struct cred *old_cred; int ret; @@ -435,10 +429,11 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len ret = file_remove_privs(file); if (ret) goto out_unlock; - - ret = ovl_real_fdget(file, &real); - if (ret) + real = ovl_real_fdget(file); + if (fd_empty(real)) { + ret = fd_err(real); goto out_unlock; + } old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = vfs_fallocate(fd_file(real), mode, offset, len); @@ -457,13 +452,13 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice) { - struct fd real; + struct fderr real; const struct cred *old_cred; int ret; - ret = ovl_real_fdget(file, &real); - if (ret) - return ret; + real = ovl_real_fdget(file); + if (fd_empty(real)) + return fd_err(real); old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = vfs_fadvise(fd_file(real), offset, len, advice); @@ -485,7 +480,7 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in, loff_t len, unsigned int flags, enum ovl_copyop op) { struct inode *inode_out = file_inode(file_out); - struct fd real_in, real_out; + struct fderr real_in, real_out; const struct cred *old_cred; loff_t ret; @@ -498,13 +493,16 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in, goto out_unlock; } - ret = ovl_real_fdget(file_out, &real_out); - if (ret) + real_out = ovl_real_fdget(file_out); + if (fd_empty(real_out)) { + ret = fd_err(real_out); goto out_unlock; + } - ret = ovl_real_fdget(file_in, &real_in); - if (ret) { + real_in = ovl_real_fdget(file_in); + if (fd_empty(real_in)) { fdput(real_out); + ret = fd_err(real_in); goto out_unlock; } @@ -577,13 +575,13 @@ static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in, static int ovl_flush(struct file *file, fl_owner_t id) { - struct fd real; + struct fderr real; const struct cred *old_cred; - int err; + int err = 0; - err = ovl_real_fdget(file, &real); - if (err) - return err; + real = ovl_real_fdget(file); + if (fd_empty(real)) + return fd_err(real); if (fd_file(real)->f_op->flush) { old_cred = ovl_override_creds(file_inode(file)->i_sb); diff --git a/include/linux/file.h b/include/linux/file.h index f98de143245a..d85352523368 100644 --- a/include/linux/file.h +++ b/include/linux/file.h @@ -44,13 +44,26 @@ static inline void fput_light(struct file *file, int fput_needed) struct fd { unsigned long word; }; + +/* either a reference to struct file + flags + * (cloned vs. borrowed, pos locked), with + * flags stored in lower bits of value, + * or an error (represented by small negative value). + */ +struct fderr { + unsigned long word; +}; + #define FDPUT_FPUT 1 #define FDPUT_POS_UNLOCK 2 +#define fd_empty(f) _Generic((f), \ + struct fd: unlikely(!(f).word), \ + struct fderr: IS_ERR_VALUE((f).word)) #define fd_file(f) ((struct file *)((f).word & ~(FDPUT_FPUT|FDPUT_POS_UNLOCK))) -static inline bool fd_empty(struct fd f) +static inline long fd_err(struct fderr f) { - return unlikely(!f.word); + return (long)f.word; } #define EMPTY_FD (struct fd){0} @@ -63,11 +76,25 @@ static inline struct fd CLONED_FD(struct file *f) return (struct fd){(unsigned long)f | FDPUT_FPUT}; } -static inline void fdput(struct fd fd) +static inline struct fderr ERR_FDERR(long n) +{ + return (struct fderr){(unsigned long)n}; +} +static inline struct fderr BORROWED_FDERR(struct file *f) { - if (fd.word & FDPUT_FPUT) - fput(fd_file(fd)); + return (struct fderr){(unsigned long)f}; } +static inline struct fderr CLONED_FDERR(struct file *f) +{ + if (IS_ERR(f)) + return BORROWED_FDERR(f); + return (struct fderr){(unsigned long)f | FDPUT_FPUT}; +} + +#define fdput(f) (void) (_Generic((f), \ + struct fderr: IS_ERR_VALUE((f).word), \ + struct fd: true) && \ + ((f).word & FDPUT_FPUT) && (fput(fd_file(f)),0)) extern struct file *fget(unsigned int fd); extern struct file *fget_raw(unsigned int fd);
Similar to struct fd; unlike struct fd, it can represent error values. Accessors: * fd_empty(f): true if f represents an error * fd_file(f): just as for struct fd it yields a pointer to struct file if fd_empty(f) is false. If fd_empty(f) is true, fd_file(f) is guaranteed _not_ to be an address of any object (IS_ERR() will be true in that case) * fd_err(f): if f represents an error, returns that error, otherwise the return value is junk. Constructors: * ERR_FDERR(-E...): an instance encoding given error [ERR_FDERR, perhaps?] * BORROWED_FDERR(file): if file points to a struct file instance, return a struct fderr representing that file reference with no flags set. if file is an ERR_PTR(-E...), return a struct fderr representing that error. file MUST NOT be NULL. * CLONED_FDERR(file): similar, but in case when file points to a struct file instance, set FDPUT_FPUT in flags. Same destructor as for struct fd; I'm not entirely convinced that playing with _Generic is a good idea here, but for now let's go that way... See fs/overlayfs/file.c for example of use. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> --- fs/overlayfs/file.c | 128 +++++++++++++++++++++---------------------- include/linux/file.h | 37 +++++++++++-- 2 files changed, 95 insertions(+), 70 deletions(-)