[PATCH 1/1] xfs: introduce new file range commit ioctls

Darrick J. Wong
2024-08-23T00:01:23Z

From: Darrick J. Wong <djwong@kernel.org>

This patch introduces two more new ioctls to manage atomic updates to
file contents -- XFS_IOC_START_COMMIT and XFS_IOC_COMMIT_RANGE. The
commit mechanism here is exactly the same as what XFS_IOC_EXCHANGE_RANGE
does, but with the additional requirement that file2 cannot have changed
since some sampling point. The start-commit ioctl performs the sampling
of file attributes.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/libxfs/xfs_fs.h | 26 +++++++++
fs/xfs/xfs_exchrange.c | 143 ++++++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_exchrange.h | 16 +++++
fs/xfs/xfs_ioctl.c | 4 +
fs/xfs/xfs_trace.h | 57 +++++++++++++++++++
5 files changed, 243 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
index 454b63ef72016..c85c8077fac39 100644
--- a/fs/xfs/libxfs/xfs_fs.h
+++ b/fs/xfs/libxfs/xfs_fs.h
@@ -825,6 +825,30 @@ struct xfs_exchange_range {
__u64 flags; /* see XFS_EXCHANGE_RANGE_* below */
};

+/*
+ * Using the same definition of file2 as struct xfs_exchange_range, commit the
+ * contents of file1 into file2 if file2 has the same inode number, mtime, and
+ * ctime as the arguments provided to the call. The old contents of file2 will
+ * be moved to file1.
+ *
+ * Returns -EBUSY if there isn't an exact match for the file2 fields.
+ *
+ * Filesystems must be able to restart and complete the operation even after
+ * the system goes down.
+ */
+struct xfs_commit_range {
+ __s32 file1_fd;
+ __u32 pad; /* must be zeroes */
+ __u64 file1_offset; /* file1 offset, bytes */
+ __u64 file2_offset; /* file2 offset, bytes */
+ __u64 length; /* bytes to exchange */
+
+ __u64 flags; /* see XFS_EXCHANGE_RANGE_* below */
+
+ /* opaque file2 metadata for freshness checks */
+ __u64 file2_freshness[6];
+};
+
/*
* Exchange file data all the way to the ends of both files, and then exchange
* the file sizes. This flag can be used to replace a file's contents with a
@@ -997,6 +1021,8 @@ struct xfs_getparents_by_handle {
#define XFS_IOC_BULKSTAT _IOR ('X', 127, struct xfs_bulkstat_req)
#define XFS_IOC_INUMBERS _IOR ('X', 128, struct xfs_inumbers_req)
#define XFS_IOC_EXCHANGE_RANGE _IOW ('X', 129, struct xfs_exchange_range)
+#define XFS_IOC_START_COMMIT _IOR ('X', 130, struct xfs_commit_range)
+#define XFS_IOC_COMMIT_RANGE _IOW ('X', 131, struct xfs_commit_range)
/* XFS_IOC_GETFSUUID ---------- deprecated 140 */

diff --git a/fs/xfs/xfs_exchrange.c b/fs/xfs/xfs_exchrange.c
index c8a655c92c92f..d0889190ab7ff 100644
--- a/fs/xfs/xfs_exchrange.c
+++ b/fs/xfs/xfs_exchrange.c
@@ -72,6 +72,34 @@ xfs_exchrange_estimate(
return error;
}

+/*
+ * Check that file2's metadata agree with the snapshot that we took for the
+ * range commit request.
+ *
+ * This should be called after the filesystem has locked /all/ inode metadata
+ * against modification.
+ */
+STATIC int
+xfs_exchrange_check_freshness(
+ const struct xfs_exchrange *fxr,
+ struct xfs_inode *ip2)
+{
+ struct inode *inode2 = VFS_I(ip2);
+ struct timespec64 ctime = inode_get_ctime(inode2);
+ struct timespec64 mtime = inode_get_mtime(inode2);
+
+ trace_xfs_exchrange_freshness(fxr, ip2);
+
+ /* Check that file2 hasn't otherwise been modified. */
+ if (fxr->file2_ino != ip2->i_ino ||
+ fxr->file2_gen != inode2->i_generation ||
+ !timespec64_equal(&fxr->file2_ctime, &ctime) ||
+ !timespec64_equal(&fxr->file2_mtime, &mtime))
+ return -EBUSY;
+
+ return 0;
+}
+
#define QRETRY_IP1 (0x1)
#define QRETRY_IP2 (0x2)

@@ -607,6 +635,12 @@ xfs_exchrange_prep(
if (error || fxr->length == 0)
return error;

+ if (fxr->flags & __XFS_EXCHANGE_RANGE_CHECK_FRESH2) {
+ error = xfs_exchrange_check_freshness(fxr, ip2);
+ if (error)
+ return error;
+ }
+
/* Attach dquots to both inodes before changing block maps. */
error = xfs_qm_dqattach(ip2);
if (error)
@@ -719,7 +753,8 @@ xfs_exchange_range(
if (fxr->file1->f_path.mnt != fxr->file2->f_path.mnt)
return -EXDEV;

- if (fxr->flags & ~XFS_EXCHANGE_RANGE_ALL_FLAGS)
+ if (fxr->flags & ~(XFS_EXCHANGE_RANGE_ALL_FLAGS |
+ __XFS_EXCHANGE_RANGE_CHECK_FRESH2))
return -EINVAL;

/* Userspace requests only honored for regular files. */
@@ -802,3 +837,109 @@ xfs_ioc_exchange_range(
fdput(file1);
return error;
}
+
+/* Opaque freshness blob for XFS_IOC_COMMIT_RANGE */
+struct xfs_commit_range_fresh {
+ xfs_fsid_t fsid; /* m_fixedfsid */
+ __u64 file2_ino; /* inode number */
+ __s64 file2_mtime; /* modification time */
+ __s64 file2_ctime; /* change time */
+ __s32 file2_mtime_nsec; /* mod time, nsec */
+ __s32 file2_ctime_nsec; /* change time, nsec */
+ __u32 file2_gen; /* inode generation */
+ __u32 magic; /* zero */
+};
+#define XCR_FRESH_MAGIC 0x444F524B /* DORK */
+
+/* Set up a commitrange operation by sampling file2's write-related attrs */
+long
+xfs_ioc_start_commit(
+ struct file *file,
+ struct xfs_commit_range __user *argp)
+{
+ struct xfs_commit_range args = { };
+ struct timespec64 ts;
+ struct xfs_commit_range_fresh *kern_f;
+ struct xfs_commit_range_fresh __user *user_f;
+ struct inode *inode2 = file_inode(file);
+ struct xfs_inode *ip2 = XFS_I(inode2);
+ const unsigned int lockflags = XFS_IOLOCK_SHARED |
+ XFS_MMAPLOCK_SHARED |
+ XFS_ILOCK_SHARED;
+
+ BUILD_BUG_ON(sizeof(struct xfs_commit_range_fresh) !=
+ sizeof(args.file2_freshness));
+
+ kern_f = (struct xfs_commit_range_fresh *)&args.file2_freshness;
+
+ memcpy(&kern_f->fsid, ip2->i_mount->m_fixedfsid, sizeof(xfs_fsid_t));
+
+ xfs_ilock(ip2, lockflags);
+ ts = inode_get_ctime(inode2);
+ kern_f->file2_ctime = ts.tv_sec;
+ kern_f->file2_ctime_nsec = ts.tv_nsec;
+ ts = inode_get_mtime(inode2);
+ kern_f->file2_mtime = ts.tv_sec;
+ kern_f->file2_mtime_nsec = ts.tv_nsec;
+ kern_f->file2_ino = ip2->i_ino;
+ kern_f->file2_gen = inode2->i_generation;
+ kern_f->magic = XCR_FRESH_MAGIC;
+ xfs_iunlock(ip2, lockflags);
+
+ user_f = (struct xfs_commit_range_fresh __user *)&argp->file2_freshness;
+ if (copy_to_user(user_f, kern_f, sizeof(*kern_f)))
+ return -EFAULT;
+
+ return 0;
+}
+
+/*
+ * Exchange file1 and file2 contents if file2 has not been written since the
+ * start commit operation.
+ */
+long
+xfs_ioc_commit_range(
+ struct file *file,
+ struct xfs_commit_range __user *argp)
+{
+ struct xfs_exchrange fxr = {
+ .file2 = file,
+ };
+ struct xfs_commit_range args;
+ struct xfs_commit_range_fresh *kern_f;
+ struct xfs_inode *ip2 = XFS_I(file_inode(file));
+ struct xfs_mount *mp = ip2->i_mount;
+ struct fd file1;
+ int error;
+
+ kern_f = (struct xfs_commit_range_fresh *)&args.file2_freshness;
+
+ if (copy_from_user(&args, argp, sizeof(args)))
+ return -EFAULT;
+ if (args.flags & ~XFS_EXCHANGE_RANGE_ALL_FLAGS)
+ return -EINVAL;
+ if (kern_f->magic != XCR_FRESH_MAGIC)
+ return -EBUSY;
+ if (memcmp(&kern_f->fsid, mp->m_fixedfsid, sizeof(xfs_fsid_t)))
+ return -EBUSY;
+
+ fxr.file1_offset = args.file1_offset;
+ fxr.file2_offset = args.file2_offset;
+ fxr.length = args.length;
+ fxr.flags = args.flags | __XFS_EXCHANGE_RANGE_CHECK_FRESH2;
+ fxr.file2_ino = kern_f->file2_ino;
+ fxr.file2_gen = kern_f->file2_gen;
+ fxr.file2_mtime.tv_sec = kern_f->file2_mtime;
+ fxr.file2_mtime.tv_nsec = kern_f->file2_mtime_nsec;
+ fxr.file2_ctime.tv_sec = kern_f->file2_ctime;
+ fxr.file2_ctime.tv_nsec = kern_f->file2_ctime_nsec;
+
+ file1 = fdget(args.file1_fd);
+ if (!file1.file)
+ return -EBADF;
+ fxr.file1 = file1.file;
+
+ error = xfs_exchange_range(&fxr);
+ fdput(file1);
+ return error;
+}
diff --git a/fs/xfs/xfs_exchrange.h b/fs/xfs/xfs_exchrange.h
index 039abcca546e8..bc1298aba806b 100644
--- a/fs/xfs/xfs_exchrange.h
+++ b/fs/xfs/xfs_exchrange.h
@@ -10,8 +10,12 @@
#define __XFS_EXCHANGE_RANGE_UPD_CMTIME1 (1ULL << 63)
#define __XFS_EXCHANGE_RANGE_UPD_CMTIME2 (1ULL << 62)

+/* Freshness check required */
+#define __XFS_EXCHANGE_RANGE_CHECK_FRESH2 (1ULL << 61)
+
#define XFS_EXCHANGE_RANGE_PRIV_FLAGS (__XFS_EXCHANGE_RANGE_UPD_CMTIME1 | \
- __XFS_EXCHANGE_RANGE_UPD_CMTIME2)
+ __XFS_EXCHANGE_RANGE_UPD_CMTIME2 | \
+ __XFS_EXCHANGE_RANGE_CHECK_FRESH2)

struct xfs_exchrange {
struct file *file1;
@@ -22,10 +26,20 @@ struct xfs_exchrange {
u64 length;

u64 flags; /* XFS_EXCHANGE_RANGE flags */
+
+ /* file2 metadata for freshness checks */
+ u64 file2_ino;
+ struct timespec64 file2_mtime;
+ struct timespec64 file2_ctime;
+ u32 file2_gen;
};

long xfs_ioc_exchange_range(struct file *file,
struct xfs_exchange_range __user *argp);
+long xfs_ioc_start_commit(struct file *file,
+ struct xfs_commit_range __user *argp);
+long xfs_ioc_commit_range(struct file *file,
+ struct xfs_commit_range __user *argp);

struct xfs_exchmaps_req;

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 6b13666d4e963..90b3ee21e7fe6 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1518,6 +1518,10 @@ xfs_file_ioctl(

case XFS_IOC_EXCHANGE_RANGE:
return xfs_ioc_exchange_range(filp, arg);
+ case XFS_IOC_START_COMMIT:
+ return xfs_ioc_start_commit(filp, arg);
+ case XFS_IOC_COMMIT_RANGE:
+ return xfs_ioc_commit_range(filp, arg);

default:
return -ENOTTY;
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 180ce697305a9..4cf0fa71ba9ce 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -4926,7 +4926,8 @@ DEFINE_INODE_ERROR_EVENT(xfs_exchrange_error);
{ XFS_EXCHANGE_RANGE_DRY_RUN, "DRY_RUN" }, \
{ XFS_EXCHANGE_RANGE_FILE1_WRITTEN, "F1_WRITTEN" }, \
{ __XFS_EXCHANGE_RANGE_UPD_CMTIME1, "CMTIME1" }, \
- { __XFS_EXCHANGE_RANGE_UPD_CMTIME2, "CMTIME2" }
+ { __XFS_EXCHANGE_RANGE_UPD_CMTIME2, "CMTIME2" }, \
+ { __XFS_EXCHANGE_RANGE_CHECK_FRESH2, "FRESH2" }

/* file exchange-range tracepoint class */
DECLARE_EVENT_CLASS(xfs_exchrange_class,
@@ -4986,6 +4987,60 @@ DEFINE_EXCHRANGE_EVENT(xfs_exchrange_prep);
DEFINE_EXCHRANGE_EVENT(xfs_exchrange_flush);
DEFINE_EXCHRANGE_EVENT(xfs_exchrange_mappings);

+TRACE_EVENT(xfs_exchrange_freshness,
+ TP_PROTO(const struct xfs_exchrange *fxr, struct xfs_inode *ip2),
+ TP_ARGS(fxr, ip2),
+ TP_STRUCT__entry(
+ __field(dev_t, dev)
+ __field(xfs_ino_t, ip2_ino)
+ __field(long long, ip2_mtime)
+ __field(long long, ip2_ctime)
+ __field(int, ip2_mtime_nsec)
+ __field(int, ip2_ctime_nsec)
+
+ __field(xfs_ino_t, file2_ino)
+ __field(long long, file2_mtime)
+ __field(long long, file2_ctime)
+ __field(int, file2_mtime_nsec)
+ __field(int, file2_ctime_nsec)
+ ),
+ TP_fast_assign(
+ struct timespec64 ts64;
+ struct inode *inode2 = VFS_I(ip2);
+
+ __entry->dev = inode2->i_sb->s_dev;
+ __entry->ip2_ino = ip2->i_ino;
+
+ ts64 = inode_get_ctime(inode2);
+ __entry->ip2_ctime = ts64.tv_sec;
+ __entry->ip2_ctime_nsec = ts64.tv_nsec;
+
+ ts64 = inode_get_mtime(inode2);
+ __entry->ip2_mtime = ts64.tv_sec;
+ __entry->ip2_mtime_nsec = ts64.tv_nsec;
+
+ __entry->file2_ino = fxr->file2_ino;
+ __entry->file2_mtime = fxr->file2_mtime.tv_sec;
+ __entry->file2_ctime = fxr->file2_ctime.tv_sec;
+ __entry->file2_mtime_nsec = fxr->file2_mtime.tv_nsec;
+ __entry->file2_ctime_nsec = fxr->file2_ctime.tv_nsec;
+ ),
+ TP_printk("dev %d:%d "
+ "ino 0x%llx mtime %lld:%d ctime %lld:%d -> "
+ "file 0x%llx mtime %lld:%d ctime %lld:%d",
+ MAJOR(__entry->dev), MINOR(__entry->dev),
+ __entry->ip2_ino,
+ __entry->ip2_mtime,
+ __entry->ip2_mtime_nsec,
+ __entry->ip2_ctime,
+ __entry->ip2_ctime_nsec,
+ __entry->file2_ino,
+ __entry->file2_mtime,
+ __entry->file2_mtime_nsec,
+ __entry->file2_ctime,
+ __entry->file2_ctime_nsec)
+);
+
TRACE_EVENT(xfs_exchmaps_overhead,
TP_PROTO(struct xfs_mount *mp, unsigned long long bmbt_blocks,
unsigned long long rmapbt_blocks),