| Message ID | 169997697704.4588.14555611205729567800.stgit@bazille.1015granger.net (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC] libfs: getdents() should return 0 after reaching EOD | expand |
On Tue, Nov 14, 2023 at 10:49:37AM -0500, Chuck Lever wrote: > -static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > +static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > { > struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); > XA_STATE(xas, &so_ctx->xa, ctx->pos); > @@ -437,7 +437,8 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > while (true) { > dentry = offset_find_next(&xas); > if (!dentry) > - break; > + /* readdir has reached the current EOD */ > + return (void *)0x10; Funny, you used the same bit pattern as ZERO_SIZE_PTR without using the macro ... > @@ -479,7 +481,12 @@ static int offset_readdir(struct file *file, struct dir_context *ctx) > if (!dir_emit_dots(file, ctx)) > return 0; > > - offset_iterate_dir(d_inode(dir), ctx); > + if (ctx->pos == 2) > + file->private_data = NULL; > + else if (file->private_data == (void *)0x10) > + return 0; > + > + file->private_data = offset_iterate_dir(d_inode(dir), ctx); > return 0; > } It might make more sense to use ERR_PTR(-ENOENT) or ERANGE or something that's a more understandable sentinel value?
On Tue, Nov 14, 2023 at 03:56:50PM +0000, Matthew Wilcox wrote: > On Tue, Nov 14, 2023 at 10:49:37AM -0500, Chuck Lever wrote: > > -static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > > +static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > > { > > struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); > > XA_STATE(xas, &so_ctx->xa, ctx->pos); > > @@ -437,7 +437,8 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > > while (true) { > > dentry = offset_find_next(&xas); > > if (!dentry) > > - break; > > + /* readdir has reached the current EOD */ > > + return (void *)0x10; > > Funny, you used the same bit pattern as ZERO_SIZE_PTR without using > the macro ... On purpose, it's an eye catcher because I didn't have a better idea. It obviously worked! > > @@ -479,7 +481,12 @@ static int offset_readdir(struct file *file, struct dir_context *ctx) > > if (!dir_emit_dots(file, ctx)) > > return 0; > > > > - offset_iterate_dir(d_inode(dir), ctx); > > + if (ctx->pos == 2) > > + file->private_data = NULL; > > + else if (file->private_data == (void *)0x10) > > + return 0; > > + > > + file->private_data = offset_iterate_dir(d_inode(dir), ctx); > > return 0; > > } > > It might make more sense to use ERR_PTR(-ENOENT) or ERANGE or something > that's a more understandable sentinel value? Yes, thanks. That's a better idea.
On Tue, Nov 14, 2023 at 10:49:37AM -0500, Chuck Lever wrote: > From: Chuck Lever <chuck.lever@oracle.com> > > The new directory offset helpers don't conform with the convention > of getdents() returning no more entries once a directory file > descriptor has reached the current end-of-directory. > > To address this, copy the logic from dcache_readdir() to mark the > open directory file descriptor once EOD has been reached. Rewinding > resets the mark. > > Reported-by: Tavian Barnes <tavianator@tavianator.com> > Closes: https://lore.kernel.org/linux-fsdevel/20231113180616.2831430-1-tavianator@tavianator.com/ > Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets") > Signed-off-by: Chuck Lever <chuck.lever@oracle.com> > --- > fs/libfs.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/fs/libfs.c b/fs/libfs.c > index e9440d55073c..1c866b087f0c 100644 > --- a/fs/libfs.c > +++ b/fs/libfs.c > @@ -428,7 +428,7 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) > inode->i_ino, fs_umode_to_dtype(inode->i_mode)); > } > > -static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > +static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > { > struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); > XA_STATE(xas, &so_ctx->xa, ctx->pos); > @@ -437,7 +437,8 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > while (true) { > dentry = offset_find_next(&xas); > if (!dentry) > - break; > + /* readdir has reached the current EOD */ > + return (void *)0x10; > > if (!offset_dir_emit(ctx, dentry)) { > dput(dentry); > @@ -447,6 +448,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > dput(dentry); > ctx->pos = xas.xa_index + 1; > } > + return NULL; > } > > /** > @@ -479,7 +481,12 @@ static int offset_readdir(struct file *file, struct dir_context *ctx) > if (!dir_emit_dots(file, ctx)) > return 0; > > - offset_iterate_dir(d_inode(dir), ctx); > + if (ctx->pos == 2) > + file->private_data = NULL; > + else if (file->private_data == (void *)0x10) > + return 0; > + > + file->private_data = offset_iterate_dir(d_inode(dir), ctx); I think it's usually best practice to only modify the file->private_data pointer during f_op->open and f_op->close but not override file->private_data once the file is visible to other threads. I think here it might not matter because access to file->private_data is serialized on f_pos_lock and it's not used by anything else.
On Tue, Nov 14, 2023 at 06:29:15PM +0100, Christian Brauner wrote: > I think it's usually best practice to only modify the file->private_data > pointer during f_op->open and f_op->close but not override > file->private_data once the file is visible to other threads. I think > here it might not matter because access to file->private_data is > serialized on f_pos_lock and it's not used by anything else. That is entirely up to filesystem. Warning that use of that library helper means that you can't use your ->d_fsdata for anything else - sure, but that's it.
On Tue, Nov 14, 2023 at 06:29:15PM +0100, Christian Brauner wrote: > On Tue, Nov 14, 2023 at 10:49:37AM -0500, Chuck Lever wrote: > > From: Chuck Lever <chuck.lever@oracle.com> > > > > The new directory offset helpers don't conform with the convention > > of getdents() returning no more entries once a directory file > > descriptor has reached the current end-of-directory. > > > > To address this, copy the logic from dcache_readdir() to mark the > > open directory file descriptor once EOD has been reached. Rewinding > > resets the mark. > > > > Reported-by: Tavian Barnes <tavianator@tavianator.com> > > Closes: https://lore.kernel.org/linux-fsdevel/20231113180616.2831430-1-tavianator@tavianator.com/ > > Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets") > > Signed-off-by: Chuck Lever <chuck.lever@oracle.com> > > --- > > fs/libfs.c | 13 ++++++++++--- > > 1 file changed, 10 insertions(+), 3 deletions(-) > > > > diff --git a/fs/libfs.c b/fs/libfs.c > > index e9440d55073c..1c866b087f0c 100644 > > --- a/fs/libfs.c > > +++ b/fs/libfs.c > > @@ -428,7 +428,7 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) > > inode->i_ino, fs_umode_to_dtype(inode->i_mode)); > > } > > > > -static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > > +static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > > { > > struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); > > XA_STATE(xas, &so_ctx->xa, ctx->pos); > > @@ -437,7 +437,8 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > > while (true) { > > dentry = offset_find_next(&xas); > > if (!dentry) > > - break; > > + /* readdir has reached the current EOD */ > > + return (void *)0x10; > > > > if (!offset_dir_emit(ctx, dentry)) { > > dput(dentry); > > @@ -447,6 +448,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) > > dput(dentry); > > ctx->pos = xas.xa_index + 1; > > } > > + return NULL; > > } > > > > /** > > @@ -479,7 +481,12 @@ static int offset_readdir(struct file *file, struct dir_context *ctx) > > if (!dir_emit_dots(file, ctx)) > > return 0; > > > > - offset_iterate_dir(d_inode(dir), ctx); > > + if (ctx->pos == 2) > > + file->private_data = NULL; > > + else if (file->private_data == (void *)0x10) > > + return 0; > > + > > + file->private_data = offset_iterate_dir(d_inode(dir), ctx); > > I think it's usually best practice to only modify the file->private_data > pointer during f_op->open and f_op->close but not override > file->private_data once the file is visible to other threads. I think > here it might not matter because access to file->private_data is > serialized on f_pos_lock and it's not used by anything else. I freely admit that using file->private_data this way is ugly. I was hoping to find one bit somewhere that I could use to mark the file descriptor, and file->private_data seemed the most handy. We could go back to allocating a phony dentry (d_alloc_cursor) and place the end-of-directory flag in there.
On Tue, Nov 14, 2023 at 05:57:14PM +0000, Al Viro wrote: > On Tue, Nov 14, 2023 at 06:29:15PM +0100, Christian Brauner wrote: > > > I think it's usually best practice to only modify the file->private_data > > pointer during f_op->open and f_op->close but not override > > file->private_data once the file is visible to other threads. I think > > here it might not matter because access to file->private_data is > > serialized on f_pos_lock and it's not used by anything else. > > That is entirely up to filesystem. Warning that use of that library > helper means that you can't use your ->d_fsdata for anything else - sure, > but that's it. Yes, but it's usually easier to reason about if the pointer just changes during open/close. Nothing I wrote said that it's mandated just so I'm clear.
diff --git a/fs/libfs.c b/fs/libfs.c index e9440d55073c..1c866b087f0c 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -428,7 +428,7 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) inode->i_ino, fs_umode_to_dtype(inode->i_mode)); } -static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) +static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) { struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); XA_STATE(xas, &so_ctx->xa, ctx->pos); @@ -437,7 +437,8 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) while (true) { dentry = offset_find_next(&xas); if (!dentry) - break; + /* readdir has reached the current EOD */ + return (void *)0x10; if (!offset_dir_emit(ctx, dentry)) { dput(dentry); @@ -447,6 +448,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) dput(dentry); ctx->pos = xas.xa_index + 1; } + return NULL; } /** @@ -479,7 +481,12 @@ static int offset_readdir(struct file *file, struct dir_context *ctx) if (!dir_emit_dots(file, ctx)) return 0; - offset_iterate_dir(d_inode(dir), ctx); + if (ctx->pos == 2) + file->private_data = NULL; + else if (file->private_data == (void *)0x10) + return 0; + + file->private_data = offset_iterate_dir(d_inode(dir), ctx); return 0; }