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Subject[PATCH 03/25] vfs: Allow fsinfo() to query what's in an fs_context [ver #14]
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Date
Allow fsinfo() to be used to query the filesystem attached to an fs_context
once a superblock has been created or if it comes from fspick().

The caller must specify AT_FSINFO_FROM_FSOPEN in the parameters and must
supply the fd from fsopen() as dfd and must set filename to NULL.

This is done with something like:

fd = fsopen("ext4", 0);
...
struct fsinfo_params params = {
.at_flags = AT_FSINFO_FROM_FSOPEN;
...
};
fsinfo(fd, NULL, &params, ...);

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/fsinfo.c | 46 +++++++++++++++++++++++++++++++++++++++++++-
fs/statfs.c | 2 +-
include/uapi/linux/fcntl.h | 2 ++
3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/fs/fsinfo.c b/fs/fsinfo.c
index 49b46f96dda3..c24701f994d1 100644
--- a/fs/fsinfo.c
+++ b/fs/fsinfo.c
@@ -8,6 +8,7 @@
#include <linux/security.h>
#include <linux/uaccess.h>
#include <linux/fsinfo.h>
+#include <linux/fs_context.h>
#include <uapi/linux/mount.h>
#include "internal.h"

@@ -340,6 +341,42 @@ static int vfs_fsinfo_fd(unsigned int fd, struct fsinfo_kparams *params)
return ret;
}

+/*
+ * Allow access to an fs_context object as created by fsopen() or fspick().
+ */
+static int vfs_fsinfo_fscontext(int fd, struct fsinfo_kparams *params)
+{
+ struct fs_context *fc;
+ struct fd f = fdget(fd);
+ int ret;
+
+ if (!f.file)
+ return -EBADF;
+
+ ret = -EINVAL;
+ if (f.file->f_op == &fscontext_fops)
+ goto out_f;
+ ret = -EOPNOTSUPP;
+ if (fc->ops == &legacy_fs_context_ops)
+ goto out_f;
+
+ ret = mutex_lock_interruptible(&fc->uapi_mutex);
+ if (ret == 0) {
+ ret = -EIO;
+ if (fc->root) {
+ struct path path = { .dentry = fc->root };
+
+ ret = vfs_fsinfo(&path, params);
+ }
+
+ mutex_unlock(&fc->uapi_mutex);
+ }
+
+out_f:
+ fdput(f);
+ return ret;
+}
+
/*
* Return buffer information by requestable attribute.
*
@@ -445,6 +482,9 @@ SYSCALL_DEFINE5(fsinfo,
params.request = user_params.request;
params.Nth = user_params.Nth;
params.Mth = user_params.Mth;
+
+ if ((params.at_flags & AT_FSINFO_FROM_FSOPEN) && filename)
+ return -EINVAL;
} else {
params.request = FSINFO_ATTR_STATFS;
}
@@ -453,6 +493,8 @@ SYSCALL_DEFINE5(fsinfo,
user_buf_size = 0;
user_buffer = NULL;
}
+ if ((params.at_flags & AT_FSINFO_FROM_FSOPEN) && filename)
+ return -EINVAL;

/* Allocate an appropriately-sized buffer. We will truncate the
* contents when we write the contents back to userspace.
@@ -500,7 +542,9 @@ SYSCALL_DEFINE5(fsinfo,
if (!params.buffer)
goto error_scratch;

- if (filename)
+ if (params.at_flags & AT_FSINFO_FROM_FSOPEN)
+ ret = vfs_fsinfo_fscontext(dfd, &params);
+ else if (filename)
ret = vfs_fsinfo_path(dfd, filename, &params);
else
ret = vfs_fsinfo_fd(dfd, &params);
diff --git a/fs/statfs.c b/fs/statfs.c
index eea7af6f2f22..b9b63d9f4f24 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -86,7 +86,7 @@ int vfs_statfs(const struct path *path, struct kstatfs *buf)
int error;

error = statfs_by_dentry(path->dentry, buf);
- if (!error)
+ if (!error && path->mnt)
buf->f_flags = calculate_f_flags(path->mnt);
return error;
}
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 1d338357df8a..6a2402a8fa30 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -91,6 +91,8 @@
#define AT_STATX_FORCE_SYNC 0x2000 /* - Force the attributes to be sync'd with the server */
#define AT_STATX_DONT_SYNC 0x4000 /* - Don't sync attributes with the server */

+#define AT_FSINFO_FROM_FSOPEN 0x2000 /* Examine the fs_context attached to dfd by fsopen() */
+
#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */


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