[PATCH 04/18] fsinfo: Allow retrieval of superblock devname, options and stats [ver #21]
From: David Howells
Date: Mon Aug 03 2020 - 09:38:26 EST
Provide fsinfo() attributes to retrieve superblock device name, options,
and statistics in string form. The following attributes are defined:
FSINFO_ATTR_SOURCE - Mount-specific device name
FSINFO_ATTR_CONFIGURATION - Mount options
FSINFO_ATTR_FS_STATISTICS - Filesystem statistics
FSINFO_ATTR_SOURCE could be made indexable by params->Nth to handle the
case where there is more than one source (e.g. the bcachefs filesystem).
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---
fs/fsinfo.c | 39 +++++++++++++++++++++++++++++++++++++++
fs/internal.h | 2 ++
fs/namespace.c | 41 +++++++++++++++++++++++++++++++++++++++++
include/uapi/linux/fsinfo.h | 3 +++
samples/vfs/test-fsinfo.c | 4 ++++
5 files changed, 89 insertions(+)
diff --git a/fs/fsinfo.c b/fs/fsinfo.c
index 79c222d465d8..aef7a736e8fc 100644
--- a/fs/fsinfo.c
+++ b/fs/fsinfo.c
@@ -231,6 +231,42 @@ static int fsinfo_generic_volume_id(struct path *path, struct fsinfo_context *ct
return fsinfo_string(path->dentry->d_sb->s_id, ctx);
}
+/*
+ * Retrieve the superblock configuration (mount options) as a comma-separated
+ * string. The initial comma is stripped off and NUL termination is added.
+ */
+static int fsinfo_generic_seq_read(struct path *path, struct fsinfo_context *ctx)
+{
+ struct super_block *sb = path->dentry->d_sb;
+ struct seq_file m = {
+ .buf = ctx->buffer,
+ .size = ctx->buf_size - 1,
+ };
+ int ret = 0;
+
+ switch (ctx->requested_attr) {
+ case FSINFO_ATTR_CONFIGURATION:
+ seq_puts(&m, sb_rdonly(sb) ? "ro" : "rw");
+ ret = security_sb_show_options(&m, sb);
+ if (!ret && sb->s_op->show_options)
+ ret = sb->s_op->show_options(&m, path->mnt->mnt_root);
+ break;
+
+ case FSINFO_ATTR_FS_STATISTICS:
+ if (sb->s_op->show_stats)
+ ret = sb->s_op->show_stats(&m, path->mnt->mnt_root);
+ break;
+ }
+
+ if (ret < 0)
+ return ret;
+ if (seq_has_overflowed(&m))
+ return ctx->buf_size + PAGE_SIZE;
+
+ ((char *)ctx->buffer)[ctx->skip + m.count] = 0;
+ return m.count + 1;
+}
+
static const struct fsinfo_attribute fsinfo_common_attributes[] = {
FSINFO_VSTRUCT (FSINFO_ATTR_STATFS, fsinfo_generic_statfs),
FSINFO_VSTRUCT (FSINFO_ATTR_IDS, fsinfo_generic_ids),
@@ -240,6 +276,9 @@ static const struct fsinfo_attribute fsinfo_common_attributes[] = {
FSINFO_STRING (FSINFO_ATTR_VOLUME_ID, fsinfo_generic_volume_id),
FSINFO_VSTRUCT (FSINFO_ATTR_VOLUME_UUID, fsinfo_generic_volume_uuid),
FSINFO_VSTRUCT (FSINFO_ATTR_FEATURES, fsinfo_generic_features),
+ FSINFO_STRING (FSINFO_ATTR_SOURCE, fsinfo_generic_mount_source),
+ FSINFO_STRING (FSINFO_ATTR_CONFIGURATION, fsinfo_generic_seq_read),
+ FSINFO_STRING (FSINFO_ATTR_FS_STATISTICS, fsinfo_generic_seq_read),
FSINFO_LIST (FSINFO_ATTR_FSINFO_ATTRIBUTES, (void *)123UL),
FSINFO_VSTRUCT_N(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO, (void *)123UL),
diff --git a/fs/internal.h b/fs/internal.h
index ea60d864a8cb..0b57da498f06 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -89,6 +89,8 @@ extern int __mnt_want_write_file(struct file *);
extern void __mnt_drop_write_file(struct file *);
extern void dissolve_on_fput(struct vfsmount *);
+extern int fsinfo_generic_mount_source(struct path *, struct fsinfo_context *);
+
/*
* fs_struct.c
*/
diff --git a/fs/namespace.c b/fs/namespace.c
index 73ff5bf0c9af..ead8d1a16610 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -30,6 +30,7 @@
#include <uapi/linux/mount.h>
#include <linux/fs_context.h>
#include <linux/shmem_fs.h>
+#include <linux/fsinfo.h>
#include "pnode.h"
#include "internal.h"
@@ -4111,3 +4112,43 @@ const struct proc_ns_operations mntns_operations = {
.install = mntns_install,
.owner = mntns_owner,
};
+
+#ifdef CONFIG_FSINFO
+static inline void mangle(struct seq_file *m, const char *s)
+{
+ seq_escape(m, s, " \t\n\\");
+}
+
+/*
+ * Return the mount source/device name as seen from this mountpoint. Shared
+ * mounts may vary here and the filesystem is permitted to substitute its own
+ * rendering.
+ */
+int fsinfo_generic_mount_source(struct path *path, struct fsinfo_context *ctx)
+{
+ struct super_block *sb = path->mnt->mnt_sb;
+ struct mount *mnt = real_mount(path->mnt);
+ struct seq_file m = {
+ .buf = ctx->buffer,
+ .size = ctx->buf_size - 1,
+ };
+ int ret;
+
+ if (sb->s_op->show_devname) {
+ ret = sb->s_op->show_devname(&m, mnt->mnt.mnt_root);
+ if (ret < 0)
+ return ret;
+ } else {
+ if (!mnt->mnt_devname)
+ return fsinfo_string("none", ctx);
+ mangle(&m, mnt->mnt_devname);
+ }
+
+ if (seq_has_overflowed(&m))
+ return ctx->buf_size + PAGE_SIZE;
+
+ ((char *)ctx->buffer)[m.count] = 0;
+ return m.count + 1;
+}
+
+#endif /* CONFIG_FSINFO */
diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
index b8b2c836267b..a27e92b68266 100644
--- a/include/uapi/linux/fsinfo.h
+++ b/include/uapi/linux/fsinfo.h
@@ -24,6 +24,9 @@
#define FSINFO_ATTR_VOLUME_UUID 0x06 /* Volume UUID (LE uuid) */
#define FSINFO_ATTR_VOLUME_NAME 0x07 /* Volume name (string) */
#define FSINFO_ATTR_FEATURES 0x08 /* Filesystem features (bits) */
+#define FSINFO_ATTR_SOURCE 0x09 /* Superblock source/device name (string) */
+#define FSINFO_ATTR_CONFIGURATION 0x0a /* Superblock configuration/options (string) */
+#define FSINFO_ATTR_FS_STATISTICS 0x0b /* Superblock filesystem statistics (string) */
#define FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO 0x100 /* Information about attr N (for path) */
#define FSINFO_ATTR_FSINFO_ATTRIBUTES 0x101 /* List of supported attrs (for path) */
diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
index c5932109f683..634f30b7e67f 100644
--- a/samples/vfs/test-fsinfo.c
+++ b/samples/vfs/test-fsinfo.c
@@ -364,6 +364,10 @@ static const struct fsinfo_attribute fsinfo_attributes[] = {
FSINFO_STRING (FSINFO_ATTR_VOLUME_ID, string),
FSINFO_VSTRUCT (FSINFO_ATTR_VOLUME_UUID, fsinfo_generic_volume_uuid),
FSINFO_STRING (FSINFO_ATTR_VOLUME_NAME, string),
+ FSINFO_STRING (FSINFO_ATTR_SOURCE, string),
+ FSINFO_STRING (FSINFO_ATTR_CONFIGURATION, string),
+ FSINFO_STRING (FSINFO_ATTR_FS_STATISTICS, string),
+
FSINFO_VSTRUCT_N(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO, fsinfo_meta_attribute_info),
FSINFO_LIST (FSINFO_ATTR_FSINFO_ATTRIBUTES, fsinfo_meta_attributes),
{}