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Message-ID: <20251002125422.203598-5-b.sachdev1904@gmail.com>
Date: Thu, 2 Oct 2025 18:18:40 +0530
From: Bhavik Sachdev <b.sachdev1904@...il.com>
To: Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org,
Aleksa Sarai <cyphar@...har.com>,
Bhavik Sachdev <b.sachdev1904@...il.com>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Jan Kara <jack@...e.cz>,
John Garry <john.g.garry@...cle.com>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
"Darrick J . Wong" <djwong@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ingo Molnar <mingo@...nel.org>,
Andrei Vagin <avagin@...il.com>,
Alexander Mikhalitsyn <alexander@...alicyn.com>
Subject: [PATCH 4/4] fs/stat: export mnt_ns_id through statx
Currently, we have no good way to get mount info for the mount a given
file descriptor is on. statx only provides it's mnt_id but we would have to
call statmount with every single mnt_ns_id in order to get mount info
since we have no way of knowing the mount namespace this mnt_id belongs
to.
This patch modifies statx to also export mnt_ns_id, allowing userspace
to easily get mount info for the mount a file descriptor is on by using
a combination of statx + statmount.
```
statx(fd, “”, AT_EMPTY_PATH,
STATX_MNT_ID_UNIQUE | STATX_MNT_NS_ID, &stat);
struct mnt_id_req req = {
.mnt_id = stat.stx_mnt_id,
.mnt_ns_id = stat.stx_mnt_ns_id
};
statmount(&req, &statmount_buf, buf_size, 0);
```
Signed-off-by: Bhavik Sachdev <b.sachdev1904@...il.com>
---
fs/stat.c | 15 +++++++++++++--
include/linux/stat.h | 1 +
include/uapi/linux/stat.h | 4 +++-
tools/include/uapi/linux/stat.h | 4 +++-
4 files changed, 20 insertions(+), 4 deletions(-)
diff --git a/fs/stat.c b/fs/stat.c
index f95c1dc3eaa4..1cc29946c0c3 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -296,18 +296,28 @@ static int statx_lookup_flags(int flags)
static int vfs_statx_path(struct path *path, int flags, struct kstat *stat,
u32 request_mask)
{
+ struct mount *real_mnt;
int error = vfs_getattr(path, stat, request_mask, flags);
if (error)
return error;
+ real_mnt = real_mount(path->mnt);
+
if (request_mask & STATX_MNT_ID_UNIQUE) {
- stat->mnt_id = real_mount(path->mnt)->mnt_id_unique;
+ stat->mnt_id = real_mnt->mnt_id_unique;
stat->result_mask |= STATX_MNT_ID_UNIQUE;
} else {
- stat->mnt_id = real_mount(path->mnt)->mnt_id;
+ stat->mnt_id = real_mnt->mnt_id;
stat->result_mask |= STATX_MNT_ID;
}
+ if (request_mask & STATX_MNT_NS_ID) {
+ if (!real_mnt->mnt_ns)
+ /* returning EINVAL for now */
+ return -EINVAL;
+ stat->mnt_ns_id = real_mnt->mnt_ns->seq;
+ }
+
if (path_mounted(path))
stat->attributes |= STATX_ATTR_MOUNT_ROOT;
stat->attributes_mask |= STATX_ATTR_MOUNT_ROOT;
@@ -745,6 +755,7 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
tmp.stx_atomic_write_unit_max = stat->atomic_write_unit_max;
tmp.stx_atomic_write_segments_max = stat->atomic_write_segments_max;
tmp.stx_atomic_write_unit_max_opt = stat->atomic_write_unit_max_opt;
+ tmp.stx_mnt_ns_id = stat->mnt_ns_id;
return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
}
diff --git a/include/linux/stat.h b/include/linux/stat.h
index e3d00e7bb26d..c62b70ce30d9 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -59,6 +59,7 @@ struct kstat {
u32 atomic_write_unit_max;
u32 atomic_write_unit_max_opt;
u32 atomic_write_segments_max;
+ u64 mnt_ns_id;
};
/* These definitions are internal to the kernel for now. Mainly used by nfsd. */
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 1686861aae20..1071f5097d26 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -187,7 +187,8 @@ struct statx {
__u32 __spare2[1];
/* 0xc0 */
- __u64 __spare3[8]; /* Spare space for future expansion */
+ __u64 stx_mnt_ns_id;
+ __u64 __spare3[7]; /* Spare space for future expansion */
/* 0x100 */
};
@@ -219,6 +220,7 @@ struct statx {
#define STATX_SUBVOL 0x00008000U /* Want/got stx_subvol */
#define STATX_WRITE_ATOMIC 0x00010000U /* Want/got atomic_write_* fields */
#define STATX_DIO_READ_ALIGN 0x00020000U /* Want/got dio read alignment info */
+#define STATX_MNT_NS_ID 0x00040000U /* Want/got stx_mnt_ns_id */
#define STATX__RESERVED 0x80000000U /* Reserved for future struct statx expansion */
diff --git a/tools/include/uapi/linux/stat.h b/tools/include/uapi/linux/stat.h
index 1686861aae20..1071f5097d26 100644
--- a/tools/include/uapi/linux/stat.h
+++ b/tools/include/uapi/linux/stat.h
@@ -187,7 +187,8 @@ struct statx {
__u32 __spare2[1];
/* 0xc0 */
- __u64 __spare3[8]; /* Spare space for future expansion */
+ __u64 stx_mnt_ns_id;
+ __u64 __spare3[7]; /* Spare space for future expansion */
/* 0x100 */
};
@@ -219,6 +220,7 @@ struct statx {
#define STATX_SUBVOL 0x00008000U /* Want/got stx_subvol */
#define STATX_WRITE_ATOMIC 0x00010000U /* Want/got atomic_write_* fields */
#define STATX_DIO_READ_ALIGN 0x00020000U /* Want/got dio read alignment info */
+#define STATX_MNT_NS_ID 0x00040000U /* Want/got stx_mnt_ns_id */
#define STATX__RESERVED 0x80000000U /* Reserved for future struct statx expansion */
--
2.51.0
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