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-rw-r--r--fs/backing-file.c336
1 files changed, 336 insertions, 0 deletions
diff --git a/fs/backing-file.c b/fs/backing-file.c
new file mode 100644
index 0000000000..a681f38d84
--- /dev/null
+++ b/fs/backing-file.c
@@ -0,0 +1,336 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Common helpers for stackable filesystems and backing files.
+ *
+ * Forked from fs/overlayfs/file.c.
+ *
+ * Copyright (C) 2017 Red Hat, Inc.
+ * Copyright (C) 2023 CTERA Networks.
+ */
+
+#include <linux/fs.h>
+#include <linux/backing-file.h>
+#include <linux/splice.h>
+#include <linux/mm.h>
+
+#include "internal.h"
+
+/**
+ * backing_file_open - open a backing file for kernel internal use
+ * @user_path: path that the user reuqested to open
+ * @flags: open flags
+ * @real_path: path of the backing file
+ * @cred: credentials for open
+ *
+ * Open a backing file for a stackable filesystem (e.g., overlayfs).
+ * @user_path may be on the stackable filesystem and @real_path on the
+ * underlying filesystem. In this case, we want to be able to return the
+ * @user_path of the stackable filesystem. This is done by embedding the
+ * returned file into a container structure that also stores the stacked
+ * file's path, which can be retrieved using backing_file_user_path().
+ */
+struct file *backing_file_open(const struct path *user_path, int flags,
+ const struct path *real_path,
+ const struct cred *cred)
+{
+ struct file *f;
+ int error;
+
+ f = alloc_empty_backing_file(flags, cred);
+ if (IS_ERR(f))
+ return f;
+
+ path_get(user_path);
+ *backing_file_user_path(f) = *user_path;
+ error = vfs_open(real_path, f);
+ if (error) {
+ fput(f);
+ f = ERR_PTR(error);
+ }
+
+ return f;
+}
+EXPORT_SYMBOL_GPL(backing_file_open);
+
+struct backing_aio {
+ struct kiocb iocb;
+ refcount_t ref;
+ struct kiocb *orig_iocb;
+ /* used for aio completion */
+ void (*end_write)(struct file *);
+ struct work_struct work;
+ long res;
+};
+
+static struct kmem_cache *backing_aio_cachep;
+
+#define BACKING_IOCB_MASK \
+ (IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND)
+
+static rwf_t iocb_to_rw_flags(int flags)
+{
+ return (__force rwf_t)(flags & BACKING_IOCB_MASK);
+}
+
+static void backing_aio_put(struct backing_aio *aio)
+{
+ if (refcount_dec_and_test(&aio->ref)) {
+ fput(aio->iocb.ki_filp);
+ kmem_cache_free(backing_aio_cachep, aio);
+ }
+}
+
+static void backing_aio_cleanup(struct backing_aio *aio, long res)
+{
+ struct kiocb *iocb = &aio->iocb;
+ struct kiocb *orig_iocb = aio->orig_iocb;
+
+ if (aio->end_write)
+ aio->end_write(orig_iocb->ki_filp);
+
+ orig_iocb->ki_pos = iocb->ki_pos;
+ backing_aio_put(aio);
+}
+
+static void backing_aio_rw_complete(struct kiocb *iocb, long res)
+{
+ struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
+ struct kiocb *orig_iocb = aio->orig_iocb;
+
+ if (iocb->ki_flags & IOCB_WRITE)
+ kiocb_end_write(iocb);
+
+ backing_aio_cleanup(aio, res);
+ orig_iocb->ki_complete(orig_iocb, res);
+}
+
+static void backing_aio_complete_work(struct work_struct *work)
+{
+ struct backing_aio *aio = container_of(work, struct backing_aio, work);
+
+ backing_aio_rw_complete(&aio->iocb, aio->res);
+}
+
+static void backing_aio_queue_completion(struct kiocb *iocb, long res)
+{
+ struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
+
+ /*
+ * Punt to a work queue to serialize updates of mtime/size.
+ */
+ aio->res = res;
+ INIT_WORK(&aio->work, backing_aio_complete_work);
+ queue_work(file_inode(aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq,
+ &aio->work);
+}
+
+static int backing_aio_init_wq(struct kiocb *iocb)
+{
+ struct super_block *sb = file_inode(iocb->ki_filp)->i_sb;
+
+ if (sb->s_dio_done_wq)
+ return 0;
+
+ return sb_init_dio_done_wq(sb);
+}
+
+
+ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
+ struct kiocb *iocb, int flags,
+ struct backing_file_ctx *ctx)
+{
+ struct backing_aio *aio = NULL;
+ const struct cred *old_cred;
+ ssize_t ret;
+
+ if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
+ return -EIO;
+
+ if (!iov_iter_count(iter))
+ return 0;
+
+ if (iocb->ki_flags & IOCB_DIRECT &&
+ !(file->f_mode & FMODE_CAN_ODIRECT))
+ return -EINVAL;
+
+ old_cred = override_creds(ctx->cred);
+ if (is_sync_kiocb(iocb)) {
+ rwf_t rwf = iocb_to_rw_flags(flags);
+
+ ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
+ } else {
+ ret = -ENOMEM;
+ aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
+ if (!aio)
+ goto out;
+
+ aio->orig_iocb = iocb;
+ kiocb_clone(&aio->iocb, iocb, get_file(file));
+ aio->iocb.ki_complete = backing_aio_rw_complete;
+ refcount_set(&aio->ref, 2);
+ ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
+ backing_aio_put(aio);
+ if (ret != -EIOCBQUEUED)
+ backing_aio_cleanup(aio, ret);
+ }
+out:
+ revert_creds(old_cred);
+
+ if (ctx->accessed)
+ ctx->accessed(ctx->user_file);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(backing_file_read_iter);
+
+ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
+ struct kiocb *iocb, int flags,
+ struct backing_file_ctx *ctx)
+{
+ const struct cred *old_cred;
+ ssize_t ret;
+
+ if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
+ return -EIO;
+
+ if (!iov_iter_count(iter))
+ return 0;
+
+ ret = file_remove_privs(ctx->user_file);
+ if (ret)
+ return ret;
+
+ if (iocb->ki_flags & IOCB_DIRECT &&
+ !(file->f_mode & FMODE_CAN_ODIRECT))
+ return -EINVAL;
+
+ /*
+ * Stacked filesystems don't support deferred completions, don't copy
+ * this property in case it is set by the issuer.
+ */
+ flags &= ~IOCB_DIO_CALLER_COMP;
+
+ old_cred = override_creds(ctx->cred);
+ if (is_sync_kiocb(iocb)) {
+ rwf_t rwf = iocb_to_rw_flags(flags);
+
+ ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf);
+ if (ctx->end_write)
+ ctx->end_write(ctx->user_file);
+ } else {
+ struct backing_aio *aio;
+
+ ret = backing_aio_init_wq(iocb);
+ if (ret)
+ goto out;
+
+ ret = -ENOMEM;
+ aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
+ if (!aio)
+ goto out;
+
+ aio->orig_iocb = iocb;
+ aio->end_write = ctx->end_write;
+ kiocb_clone(&aio->iocb, iocb, get_file(file));
+ aio->iocb.ki_flags = flags;
+ aio->iocb.ki_complete = backing_aio_queue_completion;
+ refcount_set(&aio->ref, 2);
+ ret = vfs_iocb_iter_write(file, &aio->iocb, iter);
+ backing_aio_put(aio);
+ if (ret != -EIOCBQUEUED)
+ backing_aio_cleanup(aio, ret);
+ }
+out:
+ revert_creds(old_cred);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(backing_file_write_iter);
+
+ssize_t backing_file_splice_read(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe, size_t len,
+ unsigned int flags,
+ struct backing_file_ctx *ctx)
+{
+ const struct cred *old_cred;
+ ssize_t ret;
+
+ if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
+ return -EIO;
+
+ old_cred = override_creds(ctx->cred);
+ ret = vfs_splice_read(in, ppos, pipe, len, flags);
+ revert_creds(old_cred);
+
+ if (ctx->accessed)
+ ctx->accessed(ctx->user_file);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(backing_file_splice_read);
+
+ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
+ struct file *out, loff_t *ppos, size_t len,
+ unsigned int flags,
+ struct backing_file_ctx *ctx)
+{
+ const struct cred *old_cred;
+ ssize_t ret;
+
+ if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
+ return -EIO;
+
+ ret = file_remove_privs(ctx->user_file);
+ if (ret)
+ return ret;
+
+ old_cred = override_creds(ctx->cred);
+ file_start_write(out);
+ ret = iter_file_splice_write(pipe, out, ppos, len, flags);
+ file_end_write(out);
+ revert_creds(old_cred);
+
+ if (ctx->end_write)
+ ctx->end_write(ctx->user_file);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(backing_file_splice_write);
+
+int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
+ struct backing_file_ctx *ctx)
+{
+ const struct cred *old_cred;
+ int ret;
+
+ if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||
+ WARN_ON_ONCE(ctx->user_file != vma->vm_file))
+ return -EIO;
+
+ if (!file->f_op->mmap)
+ return -ENODEV;
+
+ vma_set_file(vma, file);
+
+ old_cred = override_creds(ctx->cred);
+ ret = call_mmap(vma->vm_file, vma);
+ revert_creds(old_cred);
+
+ if (ctx->accessed)
+ ctx->accessed(ctx->user_file);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(backing_file_mmap);
+
+static int __init backing_aio_init(void)
+{
+ backing_aio_cachep = kmem_cache_create("backing_aio",
+ sizeof(struct backing_aio),
+ 0, SLAB_HWCACHE_ALIGN, NULL);
+ if (!backing_aio_cachep)
+ return -ENOMEM;
+
+ return 0;
+}
+fs_initcall(backing_aio_init);