| Message ID | 170007970281.4975.12356401645395490640.stgit@bazille.1015granger.net (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] libfs: getdents() should return 0 after reaching EOD | expand |
On Wed, Nov 15, 2023 at 03:22:52PM -0500, Chuck Lever wrote: > static int offset_readdir(struct file *file, struct dir_context *ctx) > { > + struct dentry *cursor = file->private_data; > struct dentry *dir = file->f_path.dentry; > > lockdep_assert_held(&d_inode(dir)->i_rwsem); > @@ -479,11 +481,19 @@ 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) > + cursor->d_flags &= ~DCACHE_EOD; > + else if (cursor->d_flags & DCACHE_EOD) > + return 0; > + > + if (offset_iterate_dir(d_inode(dir), ctx)) > + cursor->d_flags |= DCACHE_EOD; This is simply grotesque - "it's better to keep ->private_data constant, so we will allocate a dentry, just to store the one bit of data we need to keep track of; oh, and let's grab a bit out of ->d_flags, while we are at it; we will ignore the usual locking rules for ->d_flags modifications, 'cause it's all serialized on ->f_pos_lock". No. If nothing else, this is harder to follow than the original. It's far easier to verify that these struct file instances only use ->private_data as a flag and these accesses are serialized on ->f_pos_lock as claimed than go through the accesses to ->d_flags, prove that the one above is the only one that can happen to such dentries (while they are live, that is - once they are in __dentry_kill(), there will be modifications of ->d_flags) and that it can't happen to any other instances. NAKed-by: Al Viro <viro@zeniv.linux.org.uk>
> On Nov 18, 2023, at 11:28 AM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > On Wed, Nov 15, 2023 at 03:22:52PM -0500, Chuck Lever wrote: > >> static int offset_readdir(struct file *file, struct dir_context *ctx) >> { >> + struct dentry *cursor = file->private_data; >> struct dentry *dir = file->f_path.dentry; >> >> lockdep_assert_held(&d_inode(dir)->i_rwsem); >> @@ -479,11 +481,19 @@ 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) >> + cursor->d_flags &= ~DCACHE_EOD; >> + else if (cursor->d_flags & DCACHE_EOD) >> + return 0; >> + >> + if (offset_iterate_dir(d_inode(dir), ctx)) >> + cursor->d_flags |= DCACHE_EOD; > > This is simply grotesque - "it's better to keep ->private_data constant, > so we will allocate a dentry, just to store the one bit of data we need to > keep track of; oh, and let's grab a bit out of ->d_flags, while we are at it; > we will ignore the usual locking rules for ->d_flags modifications, 'cause > it's all serialized on ->f_pos_lock". > > No. If nothing else, this is harder to follow than the original. No argument from me. > It's > far easier to verify that these struct file instances only use ->private_data > as a flag and these accesses are serialized on ->f_pos_lock as claimed > than go through the accesses to ->d_flags, prove that the one above is > the only one that can happen to such dentries (while they are live, that > is - once they are in __dentry_kill(), there will be modifications of ->d_flags) > and that it can't happen to any other instances. > > NAKed-by: Al Viro <viro@zeniv.linux.org.uk> Fair enough. Are you comfortable enough with v1 to Ack it, or do you want me to continue looking for another mechanism for marking the end-of-directory stream? -- Chuck Lever
diff --git a/fs/libfs.c b/fs/libfs.c index e9440d55073c..d4df19b1b666 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 bool 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 +437,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) while (true) { dentry = offset_find_next(&xas); if (!dentry) - break; + return true; if (!offset_dir_emit(ctx, dentry)) { dput(dentry); @@ -447,6 +447,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) dput(dentry); ctx->pos = xas.xa_index + 1; } + return false; } /** @@ -472,6 +473,7 @@ static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx) */ static int offset_readdir(struct file *file, struct dir_context *ctx) { + struct dentry *cursor = file->private_data; struct dentry *dir = file->f_path.dentry; lockdep_assert_held(&d_inode(dir)->i_rwsem); @@ -479,11 +481,19 @@ 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) + cursor->d_flags &= ~DCACHE_EOD; + else if (cursor->d_flags & DCACHE_EOD) + return 0; + + if (offset_iterate_dir(d_inode(dir), ctx)) + cursor->d_flags |= DCACHE_EOD; return 0; } const struct file_operations simple_offset_dir_operations = { + .open = dcache_dir_open, + .release = dcache_dir_close, .llseek = offset_dir_llseek, .iterate_shared = offset_readdir, .read = generic_read_dir, diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 3da2f0545d5d..ee1757001583 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -208,6 +208,7 @@ struct dentry_operations { #define DCACHE_FALLTHRU 0x01000000 /* Fall through to lower layer */ #define DCACHE_NOKEY_NAME 0x02000000 /* Encrypted name encoded without key */ #define DCACHE_OP_REAL 0x04000000 +#define DCACHE_EOD 0x08000000 /* Reached end-of-directory */ #define DCACHE_PAR_LOOKUP 0x10000000 /* being looked up (with parent locked shared) */ #define DCACHE_DENTRY_CURSOR 0x20000000