[PATCH] fuse: don't allow signals to interrupt getdents copying

[Miklos Szeredi <mszeredi@redhat.com>]

When getting the directory contents, the entries are first fetched to a
kernel buffer, then they are copied to userspace with dir_emit().  This
second phase is non-blocking as long as the userspace buffer is not paged
out, making it interruptible makes zero sense.

Overload d_type as flags, since it only uses 4 bits from 32.

Reviewed-by: Bernd Schubert <bschubert@ddn.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
rfc -> v1:
  Added BUILD_BUG_ON() to verify no overlap with S_DT_MASK

 fs/fuse/readdir.c  |  4 ++--
 fs/readdir.c       | 18 +++++++++++++++---
 include/linux/fs.h |  3 +++
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c
index 46b7146f2c0d..59defad9d05e 100644
--- a/fs/fuse/readdir.c
+++ b/fs/fuse/readdir.c
@@ -120,7 +120,7 @@ static bool fuse_emit(struct file *file, struct dir_context *ctx,
 		fuse_add_dirent_to_cache(file, dirent, ctx->pos);
 
 	return dir_emit(ctx, dirent->name, dirent->namelen, dirent->ino,
-			dirent->type);
+			dirent->type | FILLDIR_FLAG_NOINTR);
 }
 
 static int parse_dirfile(char *buf, size_t nbytes, struct file *file,
@@ -422,7 +422,7 @@ static enum fuse_parse_result fuse_parse_cache(struct fuse_file *ff,
 		if (ff->readdir.pos == ctx->pos) {
 			res = FOUND_SOME;
 			if (!dir_emit(ctx, dirent->name, dirent->namelen,
-				      dirent->ino, dirent->type))
+				      dirent->ino, dirent->type | FILLDIR_FLAG_NOINTR))
 				return FOUND_ALL;
 			ctx->pos = dirent->off;
 		}
diff --git a/fs/readdir.c b/fs/readdir.c
index 0038efda417b..857d402bc531 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -266,6 +266,10 @@ static bool filldir(struct dir_context *ctx, const char *name, int namlen,
 	int reclen = ALIGN(offsetof(struct linux_dirent, d_name) + namlen + 2,
 		sizeof(long));
 	int prev_reclen;
+	unsigned int flags = d_type;
+
+	BUILD_BUG_ON(FILLDIR_FLAG_NOINTR & S_DT_MASK);
+	d_type &= S_DT_MASK;
 
 	buf->error = verify_dirent_name(name, namlen);
 	if (unlikely(buf->error))
@@ -279,7 +283,7 @@ static bool filldir(struct dir_context *ctx, const char *name, int namlen,
 		return false;
 	}
 	prev_reclen = buf->prev_reclen;
-	if (prev_reclen && signal_pending(current))
+	if (!(flags & FILLDIR_FLAG_NOINTR) && prev_reclen && signal_pending(current))
 		return false;
 	dirent = buf->current_dir;
 	prev = (void __user *) dirent - prev_reclen;
@@ -351,6 +355,10 @@ static bool filldir64(struct dir_context *ctx, const char *name, int namlen,
 	int reclen = ALIGN(offsetof(struct linux_dirent64, d_name) + namlen + 1,
 		sizeof(u64));
 	int prev_reclen;
+	unsigned int flags = d_type;
+
+	BUILD_BUG_ON(FILLDIR_FLAG_NOINTR & S_DT_MASK);
+	d_type &= S_DT_MASK;
 
 	buf->error = verify_dirent_name(name, namlen);
 	if (unlikely(buf->error))
@@ -359,7 +367,7 @@ static bool filldir64(struct dir_context *ctx, const char *name, int namlen,
 	if (reclen > buf->count)
 		return false;
 	prev_reclen = buf->prev_reclen;
-	if (prev_reclen && signal_pending(current))
+	if (!(flags & FILLDIR_FLAG_NOINTR) && prev_reclen && signal_pending(current))
 		return false;
 	dirent = buf->current_dir;
 	prev = (void __user *)dirent - prev_reclen;
@@ -513,6 +521,10 @@ static bool compat_filldir(struct dir_context *ctx, const char *name, int namlen
 	int reclen = ALIGN(offsetof(struct compat_linux_dirent, d_name) +
 		namlen + 2, sizeof(compat_long_t));
 	int prev_reclen;
+	unsigned int flags = d_type;
+
+	BUILD_BUG_ON(FILLDIR_FLAG_NOINTR & S_DT_MASK);
+	d_type &= S_DT_MASK;
 
 	buf->error = verify_dirent_name(name, namlen);
 	if (unlikely(buf->error))
@@ -526,7 +538,7 @@ static bool compat_filldir(struct dir_context *ctx, const char *name, int namlen
 		return false;
 	}
 	prev_reclen = buf->prev_reclen;
-	if (prev_reclen && signal_pending(current))
+	if (!(flags & FILLDIR_FLAG_NOINTR) && prev_reclen && signal_pending(current))
 		return false;
 	dirent = buf->current_dir;
 	prev = (void __user *) dirent - prev_reclen;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 016b0fe1536e..0f2a1a572e3a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2073,6 +2073,9 @@ struct dir_context {
 	loff_t pos;
 };
 
+/* If OR-ed with d_type, pending signals are not checked */
+#define FILLDIR_FLAG_NOINTR	0x1000
+
 /*
  * These flags let !MMU mmap() govern direct device mapping vs immediate
  * copying more easily for MAP_PRIVATE, especially for ROM filesystems.
-- 
2.49.0