readdir: supply dir_context.count as readdir buffer size hint

This is a preparation for large readdir buffers in fuse.

Simply setting the fuse buffer size to the userspace buffer size should
work, the record sizes are similar (fuse's is slightly larger than libc's,
so no overflow should ever happen).

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Jaco Kroon <jaco@uls.co.za>
Link: https://lore.kernel.org/20250513151012.1476536-1-mszeredi@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 14 insertions, 15 deletions

diff --git a/fs/readdir.c b/fs/readdir.c
index 857d402bc531..7764b8638978 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -222,6 +222,7 @@ SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 	CLASS(fd_pos, f)(fd);
 	struct readdir_callback buf = {
 		.ctx.actor = fillonedir,
+		.ctx.count = 1, /* Hint to fs: just one entry. */
 		.dirent = dirent
 	};
 
@@ -252,7 +253,6 @@ struct getdents_callback {
 	struct dir_context ctx;
 	struct linux_dirent __user * current_dir;
 	int prev_reclen;
-	int count;
 	int error;
 };
 
@@ -275,7 +275,7 @@ static bool filldir(struct dir_context *ctx, const char *name, int namlen,
 	if (unlikely(buf->error))
 		return false;
 	buf->error = -EINVAL;	/* only used if we fail.. */
-	if (reclen > buf->count)
+	if (reclen > ctx->count)
 		return false;
 	d_ino = ino;
 	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
@@ -300,7 +300,7 @@ static bool filldir(struct dir_context *ctx, const char *name, int namlen,
 
 	buf->current_dir = (void __user *)dirent + reclen;
 	buf->prev_reclen = reclen;
-	buf->count -= reclen;
+	ctx->count -= reclen;
 	return true;
 efault_end:
 	user_write_access_end();
@@ -315,7 +315,7 @@ SYSCALL_DEFINE3(getdents, unsigned int, fd,
 	CLASS(fd_pos, f)(fd);
 	struct getdents_callback buf = {
 		.ctx.actor = filldir,
-		.count = count,
+		.ctx.count = count,
 		.current_dir = dirent
 	};
 	int error;
@@ -333,7 +333,7 @@ SYSCALL_DEFINE3(getdents, unsigned int, fd,
 		if (put_user(buf.ctx.pos, &lastdirent->d_off))
 			error = -EFAULT;
 		else
-			error = count - buf.count;
+			error = count - buf.ctx.count;
 	}
 	return error;
 }
@@ -342,7 +342,6 @@ struct getdents_callback64 {
 	struct dir_context ctx;
 	struct linux_dirent64 __user * current_dir;
 	int prev_reclen;
-	int count;
 	int error;
 };
 
@@ -364,7 +363,7 @@ static bool filldir64(struct dir_context *ctx, const char *name, int namlen,
 	if (unlikely(buf->error))
 		return false;
 	buf->error = -EINVAL;	/* only used if we fail.. */
-	if (reclen > buf->count)
+	if (reclen > ctx->count)
 		return false;
 	prev_reclen = buf->prev_reclen;
 	if (!(flags & FILLDIR_FLAG_NOINTR) && prev_reclen && signal_pending(current))
@@ -384,7 +383,7 @@ static bool filldir64(struct dir_context *ctx, const char *name, int namlen,
 
 	buf->prev_reclen = reclen;
 	buf->current_dir = (void __user *)dirent + reclen;
-	buf->count -= reclen;
+	ctx->count -= reclen;
 	return true;
 
 efault_end:
@@ -400,7 +399,7 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 	CLASS(fd_pos, f)(fd);
 	struct getdents_callback64 buf = {
 		.ctx.actor = filldir64,
-		.count = count,
+		.ctx.count = count,
 		.current_dir = dirent
 	};
 	int error;
@@ -419,7 +418,7 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 		if (put_user(d_off, &lastdirent->d_off))
 			error = -EFAULT;
 		else
-			error = count - buf.count;
+			error = count - buf.ctx.count;
 	}
 	return error;
 }
@@ -483,6 +482,7 @@ COMPAT_SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 	CLASS(fd_pos, f)(fd);
 	struct compat_readdir_callback buf = {
 		.ctx.actor = compat_fillonedir,
+		.ctx.count = 1, /* Hint to fs: just one entry. */
 		.dirent = dirent
 	};
 
@@ -507,7 +507,6 @@ struct compat_getdents_callback {
 	struct dir_context ctx;
 	struct compat_linux_dirent __user *current_dir;
 	int prev_reclen;
-	int count;
 	int error;
 };
 
@@ -530,7 +529,7 @@ static bool compat_filldir(struct dir_context *ctx, const char *name, int namlen
 	if (unlikely(buf->error))
 		return false;
 	buf->error = -EINVAL;	/* only used if we fail.. */
-	if (reclen > buf->count)
+	if (reclen > ctx->count)
 		return false;
 	d_ino = ino;
 	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
@@ -554,7 +553,7 @@ static bool compat_filldir(struct dir_context *ctx, const char *name, int namlen
 
 	buf->prev_reclen = reclen;
 	buf->current_dir = (void __user *)dirent + reclen;
-	buf->count -= reclen;
+	ctx->count -= reclen;
 	return true;
 efault_end:
 	user_write_access_end();
@@ -569,8 +568,8 @@ COMPAT_SYSCALL_DEFINE3(getdents, unsigned int, fd,
 	CLASS(fd_pos, f)(fd);
 	struct compat_getdents_callback buf = {
 		.ctx.actor = compat_filldir,
+		.ctx.count = count,
 		.current_dir = dirent,
-		.count = count
 	};
 	int error;
 
@@ -587,7 +586,7 @@ COMPAT_SYSCALL_DEFINE3(getdents, unsigned int, fd,
 		if (put_user(buf.ctx.pos, &lastdirent->d_off))
 			error = -EFAULT;
 		else
-			error = count - buf.count;
+			error = count - buf.ctx.count;
 	}
 	return error;
 }