9pfs changes:

* Fixes for file descriptor reclaiming algorithm (i.e. when running
   towards host's allowed limit of max. open file descriptors).
 
 * Additional fixes on use-after-unlink idiom (i.e. client operations on a
   file descriptor after file has been removed).
 -----BEGIN PGP SIGNATURE-----
 
 iQJLBAABCgA1FiEEltjREM96+AhPiFkBNMK1h2Wkc5UFAmgYie0XHHFlbXVfb3Nz
 QGNydWRlYnl0ZS5jb20ACgkQNMK1h2Wkc5XbDRAAq5SW7Hxifdhf1ZRBtkVOD88q
 Iw/OrMLIke4pCQwRElCDrE0mhycqyUpNX67eIye7qx0dJl2btFQUI9L6YuCDFtcG
 fPORZl51V81BOXqS8MhbK1oDxidl+cnpA8GcA1OyhYjxBifOy/x/0KG0pZVwzi0Y
 jhAIdsfeSenTE0Zzb02oh9mVmlMtKnwrSz7R0IB3Sv575CQiO76OM5B9sps1TUPu
 NrnQYBIB+EwJnI+l9NOKzNa7AUxV/S73OFCyJkQCON2ZHWiVadgXxjlX3kHyh9oL
 3uiiTdC2694jU0RaVMMSNLfdIG4YK2GkKPHM7qLYF8Kdc5QogEJifS/RoihCnZFR
 X72G7mOVo8/7goRBt3DGQCwz3eUgqTO9iPFn1hJRvx9x/CVlFi2eOP+5nHR5PMEO
 qSY2of6LziCslNXvxjjhf7HmRhlugkHqpr+UGTxwMGazr88bHKNFbsh/3BcTmWwW
 /wGRfEFse3exgFiCtoebavxbJaUeI0Y93S4KidOhhqrQFz24k2AElgFrb1gEpbht
 GWW8YEblL7Lj8mecFATXKiInHCyhVPFmuAO//Wbu9juJVcNPtl67f017bCR+90H3
 GrRJqorHrp6icGQmXSM+Qdrr3B21RZwqb3W4mdMOWN3Zg5bHPHJ6rx8BRe7qDHBH
 mWtvrsUfcL0sRW0nkgc=
 =hfW6
 -----END PGP SIGNATURE-----

Merge tag 'pull-9p-20250505' of https://github.com/cschoenebeck/qemu into staging

9pfs changes:

* Fixes for file descriptor reclaiming algorithm (i.e. when running
  towards host's allowed limit of max. open file descriptors).

* Additional fixes on use-after-unlink idiom (i.e. client operations on a
  file descriptor after file has been removed).

# -----BEGIN PGP SIGNATURE-----
#
# iQJLBAABCgA1FiEEltjREM96+AhPiFkBNMK1h2Wkc5UFAmgYie0XHHFlbXVfb3Nz
# QGNydWRlYnl0ZS5jb20ACgkQNMK1h2Wkc5XbDRAAq5SW7Hxifdhf1ZRBtkVOD88q
# Iw/OrMLIke4pCQwRElCDrE0mhycqyUpNX67eIye7qx0dJl2btFQUI9L6YuCDFtcG
# fPORZl51V81BOXqS8MhbK1oDxidl+cnpA8GcA1OyhYjxBifOy/x/0KG0pZVwzi0Y
# jhAIdsfeSenTE0Zzb02oh9mVmlMtKnwrSz7R0IB3Sv575CQiO76OM5B9sps1TUPu
# NrnQYBIB+EwJnI+l9NOKzNa7AUxV/S73OFCyJkQCON2ZHWiVadgXxjlX3kHyh9oL
# 3uiiTdC2694jU0RaVMMSNLfdIG4YK2GkKPHM7qLYF8Kdc5QogEJifS/RoihCnZFR
# X72G7mOVo8/7goRBt3DGQCwz3eUgqTO9iPFn1hJRvx9x/CVlFi2eOP+5nHR5PMEO
# qSY2of6LziCslNXvxjjhf7HmRhlugkHqpr+UGTxwMGazr88bHKNFbsh/3BcTmWwW
# /wGRfEFse3exgFiCtoebavxbJaUeI0Y93S4KidOhhqrQFz24k2AElgFrb1gEpbht
# GWW8YEblL7Lj8mecFATXKiInHCyhVPFmuAO//Wbu9juJVcNPtl67f017bCR+90H3
# GrRJqorHrp6icGQmXSM+Qdrr3B21RZwqb3W4mdMOWN3Zg5bHPHJ6rx8BRe7qDHBH
# mWtvrsUfcL0sRW0nkgc=
# =hfW6
# -----END PGP SIGNATURE-----
# gpg: Signature made Mon 05 May 2025 05:50:37 EDT
# gpg:                using RSA key 96D8D110CF7AF8084F88590134C2B58765A47395
# gpg:                issuer "qemu_oss@crudebyte.com"
# gpg: Good signature from "Christian Schoenebeck <qemu_oss@crudebyte.com>" [unknown]
# gpg: WARNING: The key's User ID is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: ECAB 1A45 4014 1413 BA38  4926 30DB 47C3 A012 D5F4
#      Subkey fingerprint: 96D8 D110 CF7A F808 4F88  5901 34C2 B587 65A4 7395

* tag 'pull-9p-20250505' of https://github.com/cschoenebeck/qemu:
  9pfs: fix 'total_open_fd' decrementation
  tests/9p: Test `Tsetattr` can truncate unlinked file
  tests/9p: add 'Tsetattr' request to test client
  9pfs: Introduce futimens file op
  9pfs: Introduce ftruncate file op
  9pfs: Don't use file descriptors in core code
  9pfs: local : Introduce local_fid_fd() helper
  9pfs: fix FD leak and reduce latency of v9fs_reclaim_fd()
  9pfs: fix concurrent v9fs_reclaim_fd() calls

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

fsdev/file-op-9p.h

@@ -129,6 +129,8 @@ struct FileOperations {
     int (*chown)(FsContext *, V9fsPath *, FsCred *);
     int (*mknod)(FsContext *, V9fsPath *, const char *, FsCred *);
     int (*utimensat)(FsContext *, V9fsPath *, const struct timespec *);
+    int (*futimens)(FsContext *ctx, int fid_type, V9fsFidOpenState *fs,
+                    const struct timespec *times);
     int (*remove)(FsContext *, const char *);
     int (*symlink)(FsContext *, const char *, V9fsPath *,
                    const char *, FsCred *);
@@ -152,6 +154,8 @@ struct FileOperations {
     int (*fstat)(FsContext *, int, V9fsFidOpenState *, struct stat *);
     int (*rename)(FsContext *, const char *, const char *);
     int (*truncate)(FsContext *, V9fsPath *, off_t);
+    int (*ftruncate)(FsContext *ctx, int fid_type, V9fsFidOpenState *fs,
+                     off_t size);
     int (*fsync)(FsContext *, int, V9fsFidOpenState *, int);
     int (*statfs)(FsContext *s, V9fsPath *path, struct statfs *stbuf);
     ssize_t (*lgetxattr)(FsContext *, V9fsPath *,
@@ -164,6 +168,7 @@ struct FileOperations {
     int (*renameat)(FsContext *ctx, V9fsPath *olddir, const char *old_name,
                     V9fsPath *newdir, const char *new_name);
     int (*unlinkat)(FsContext *ctx, V9fsPath *dir, const char *name, int flags);
+    bool (*has_valid_file_handle)(int fid_type, V9fsFidOpenState *fs);
 };
 
 #endif

hw/9pfs/9p-local.c

@@ -766,16 +766,19 @@ out:
     return err;
 }
 
+static int local_fid_fd(int fid_type, V9fsFidOpenState *fs)
+{
+    if (fid_type == P9_FID_DIR) {
+        return dirfd(fs->dir.stream);
+    } else {
+        return fs->fd;
+    }
+}
+
 static int local_fstat(FsContext *fs_ctx, int fid_type,
                        V9fsFidOpenState *fs, struct stat *stbuf)
 {
-    int err, fd;
+    int err, fd = local_fid_fd(fid_type, fs);
-
-    if (fid_type == P9_FID_DIR) {
-        fd = dirfd(fs->dir.stream);
-    } else {
-        fd = fs->fd;
-    }
 
     err = fstat(fd, stbuf);
     if (err) {
@@ -1039,6 +1042,14 @@ static int local_truncate(FsContext *ctx, V9fsPath *fs_path, off_t size)
     return ret;
 }
 
+static int local_ftruncate(FsContext *ctx, int fid_type, V9fsFidOpenState *fs,
+                           off_t size)
+{
+    int fd = local_fid_fd(fid_type, fs);
+
+    return ftruncate(fd, size);
+}
+
 static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
 {
     char *dirpath = g_path_get_dirname(fs_path->data);
@@ -1089,6 +1100,14 @@ out:
     return ret;
 }
 
+static int local_futimens(FsContext *s, int fid_type, V9fsFidOpenState *fs,
+                          const struct timespec *times)
+{
+    int fd = local_fid_fd(fid_type, fs);
+
+    return qemu_futimens(fd, times);
+}
+
 static int local_unlinkat_common(FsContext *ctx, int dirfd, const char *name,
                                  int flags)
 {
@@ -1167,13 +1186,7 @@ out:
 static int local_fsync(FsContext *ctx, int fid_type,
                        V9fsFidOpenState *fs, int datasync)
 {
-    int fd;
+    int fd = local_fid_fd(fid_type, fs);
-
-    if (fid_type == P9_FID_DIR) {
-        fd = dirfd(fs->dir.stream);
-    } else {
-        fd = fs->fd;
-    }
 
     if (datasync) {
         return qemu_fdatasync(fd);
@@ -1575,6 +1588,13 @@ static int local_parse_opts(QemuOpts *opts, FsDriverEntry *fse, Error **errp)
     return 0;
 }
 
+static bool local_has_valid_file_handle(int fid_type, V9fsFidOpenState *fs)
+{
+    return
+        (fid_type == P9_FID_FILE && fs->fd != -1) ||
+        (fid_type == P9_FID_DIR && fs->dir.stream != NULL);
+}
+
 FileOperations local_ops = {
     .parse_opts = local_parse_opts,
     .init  = local_init,
@@ -1612,4 +1632,7 @@ FileOperations local_ops = {
     .name_to_path = local_name_to_path,
     .renameat  = local_renameat,
     .unlinkat = local_unlinkat,
+    .has_valid_file_handle = local_has_valid_file_handle,
+    .ftruncate = local_ftruncate,
+    .futimens = local_futimens,
 };

hw/9pfs/9p-synth.c

@@ -356,6 +356,13 @@ static int synth_truncate(FsContext *ctx, V9fsPath *path, off_t offset)
     return -1;
 }
 
+static int synth_ftruncate(FsContext *ctx, int fid_type, V9fsFidOpenState *fs,
+                           off_t size)
+{
+    errno = ENOSYS;
+    return -1;
+}
+
 static int synth_chmod(FsContext *fs_ctx, V9fsPath *path, FsCred *credp)
 {
     errno = EPERM;
@@ -417,6 +424,13 @@ static int synth_utimensat(FsContext *fs_ctx, V9fsPath *path,
     return 0;
 }
 
+static int synth_futimens(FsContext *fs_ctx, int fid_type, V9fsFidOpenState *fs,
+                          const struct timespec *buf)
+{
+    errno = ENOSYS;
+    return -1;
+}
+
 static int synth_remove(FsContext *ctx, const char *path)
 {
     errno = EPERM;
@@ -615,6 +629,11 @@ static int synth_init(FsContext *ctx, Error **errp)
     return 0;
 }
 
+static bool synth_has_valid_file_handle(int fid_type, V9fsFidOpenState *fs)
+{
+    return false;
+}
+
 FileOperations synth_ops = {
     .init         = synth_init,
     .lstat        = synth_lstat,
@@ -650,4 +669,7 @@ FileOperations synth_ops = {
     .name_to_path = synth_name_to_path,
     .renameat     = synth_renameat,
     .unlinkat     = synth_unlinkat,
+    .has_valid_file_handle = synth_has_valid_file_handle,
+    .ftruncate    = synth_ftruncate,
+    .futimens     = synth_futimens,
 };

hw/9pfs/9p-util.h

@@ -103,6 +103,7 @@ static inline int errno_to_dotl(int err) {
 #define qemu_renameat   renameat
 #define qemu_utimensat  utimensat
 #define qemu_unlinkat   unlinkat
+#define qemu_futimens   futimens
 
 static inline void close_preserve_errno(int fd)
 {

hw/9pfs/9p.c

@@ -434,16 +434,24 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
     V9fsFidState *f;
     GHashTableIter iter;
     gpointer fid;
+    int err;
+    int nclosed = 0;
+
+    /* prevent multiple coroutines running this function simultaniously */
+    if (s->reclaiming) {
+        return;
+    }
+    s->reclaiming = true;
 
     g_hash_table_iter_init(&iter, s->fids);
 
     QSLIST_HEAD(, V9fsFidState) reclaim_list =
         QSLIST_HEAD_INITIALIZER(reclaim_list);
 
+    /* Pick FIDs to be closed, collect them on reclaim_list. */
     while (g_hash_table_iter_next(&iter, &fid, (gpointer *) &f)) {
         /*
-         * Unlink fids cannot be reclaimed. Check
+         * Unlinked fids cannot be reclaimed, skip those, and also skip fids
-         * for them and skip them. Also skip fids
          * currently being operated on.
          */
         if (f->ref || f->flags & FID_NON_RECLAIMABLE) {
@@ -493,23 +501,42 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
         }
     }
     /*
-     * Now close the fid in reclaim list. Free them if they
+     * Close the picked FIDs altogether on a background I/O driver thread. Do
-     * are already clunked.
+     * this all at once to keep latency (i.e. amount of thread hops between main
+     * thread <-> fs driver background thread) as low as possible.
      */
+    v9fs_co_run_in_worker({
+        QSLIST_FOREACH(f, &reclaim_list, reclaim_next) {
+            err = (f->fid_type == P9_FID_DIR) ?
+                s->ops->closedir(&s->ctx, &f->fs_reclaim) :
+                s->ops->close(&s->ctx, &f->fs_reclaim);
+
+            /* 'man 2 close' suggests to ignore close() errors except of EBADF */
+            if (unlikely(err && errno == EBADF)) {
+                /*
+                 * unexpected case as FIDs were picked above by having a valid
+                 * file descriptor
+                 */
+                error_report("9pfs: v9fs_reclaim_fd() WARNING: close() failed with EBADF");
+            } else {
+                /* total_open_fd must only be mutated on main thread */
+                nclosed++;
+            }
+        }
+    });
+    total_open_fd -= nclosed;
+    /* Free the closed FIDs. */
     while (!QSLIST_EMPTY(&reclaim_list)) {
         f = QSLIST_FIRST(&reclaim_list);
         QSLIST_REMOVE(&reclaim_list, f, V9fsFidState, reclaim_next);
-        if (f->fid_type == P9_FID_FILE) {
-            v9fs_co_close(pdu, &f->fs_reclaim);
-        } else if (f->fid_type == P9_FID_DIR) {
-            v9fs_co_closedir(pdu, &f->fs_reclaim);
-        }
         /*
          * Now drop the fid reference, free it
          * if clunked.
          */
         put_fid(pdu, f);
     }
+
+    s->reclaiming = false;
 }
 
 /*
@@ -1574,6 +1601,11 @@ out_nofid:
     pdu_complete(pdu, err);
 }
 
+static bool fid_has_valid_file_handle(V9fsState *s, V9fsFidState *fidp)
+{
+    return s->ops->has_valid_file_handle(fidp->fid_type, &fidp->fs);
+}
+
 static void coroutine_fn v9fs_getattr(void *opaque)
 {
     int32_t fid;
@@ -1596,9 +1628,7 @@ static void coroutine_fn v9fs_getattr(void *opaque)
         retval = -ENOENT;
         goto out_nofid;
     }
-    if ((fidp->fid_type == P9_FID_FILE && fidp->fs.fd != -1) ||
+    if (fid_has_valid_file_handle(pdu->s, fidp)) {
-        (fidp->fid_type == P9_FID_DIR && fidp->fs.dir.stream))
-    {
         retval = v9fs_co_fstat(pdu, fidp, &stbuf);
     } else {
         retval = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
@@ -1705,7 +1735,11 @@ static void coroutine_fn v9fs_setattr(void *opaque)
         } else {
             times[1].tv_nsec = UTIME_OMIT;
         }
+        if (fid_has_valid_file_handle(pdu->s, fidp)) {
+            err = v9fs_co_futimens(pdu, fidp, times);
+        } else {
             err = v9fs_co_utimensat(pdu, &fidp->path, times);
+        }
         if (err < 0) {
             goto out;
         }
@@ -1730,7 +1764,11 @@ static void coroutine_fn v9fs_setattr(void *opaque)
         }
     }
     if (v9iattr.valid & (P9_ATTR_SIZE)) {
+        if (fid_has_valid_file_handle(pdu->s, fidp)) {
+            err = v9fs_co_ftruncate(pdu, fidp, v9iattr.size);
+        } else {
             err = v9fs_co_truncate(pdu, &fidp->path, v9iattr.size);
+        }
         if (err < 0) {
             goto out;
         }
@@ -4324,6 +4362,8 @@ int v9fs_device_realize_common(V9fsState *s, const V9fsTransport *t,
     s->ctx.fst = &fse->fst;
     fsdev_throttle_init(s->ctx.fst);
 
+    s->reclaiming = false;
+
     rc = 0;
 out:
     if (rc) {

hw/9pfs/9p.h

@@ -362,6 +362,7 @@ struct V9fsState {
     uint64_t qp_ndevices; /* Amount of entries in qpd_table. */
     uint16_t qp_affix_next;
     uint64_t qp_fullpath_next;
+    bool reclaiming;
 };
 
 /* 9p2000.L open flags */

hw/9pfs/codir.c

@@ -20,6 +20,7 @@
 #include "fsdev/qemu-fsdev.h"
 #include "qemu/thread.h"
 #include "qemu/main-loop.h"
+#include "qemu/error-report.h"
 #include "coth.h"
 #include "9p-xattr.h"
 #include "9p-util.h"
@@ -353,7 +354,11 @@ int coroutine_fn v9fs_co_closedir(V9fsPDU *pdu, V9fsFidOpenState *fs)
                 err = -errno;
             }
         });
-    if (!err) {
+    /* 'man 2 close' suggests to ignore close() errors except of EBADF */
+    if (unlikely(err && errno == EBADF)) {
+        /* unexpected case as we should have checked for a valid file handle */
+        error_report("9pfs: WARNING: v9fs_co_closedir() failed with EBADF");
+    } else {
         total_open_fd--;
     }
     return err;

hw/9pfs/cofile.c

@@ -20,6 +20,7 @@
 #include "fsdev/qemu-fsdev.h"
 #include "qemu/thread.h"
 #include "qemu/main-loop.h"
+#include "qemu/error-report.h"
 #include "coth.h"
 
 int coroutine_fn v9fs_co_st_gen(V9fsPDU *pdu, V9fsPath *path, mode_t st_mode,
@@ -197,7 +198,11 @@ int coroutine_fn v9fs_co_close(V9fsPDU *pdu, V9fsFidOpenState *fs)
                 err = -errno;
             }
         });
-    if (!err) {
+    /* 'man 2 close' suggests to ignore close() errors except of EBADF */
+    if (unlikely(err && errno == EBADF)) {
+        /* unexpected case as we should have checked for a valid file handle */
+        error_report("9pfs: WARNING: v9fs_co_close() failed with EBADF");
+    } else {
         total_open_fd--;
     }
     return err;

hw/9pfs/cofs.c

@@ -139,6 +139,25 @@ int coroutine_fn v9fs_co_utimensat(V9fsPDU *pdu, V9fsPath *path,
     return err;
 }
 
+int coroutine_fn v9fs_co_futimens(V9fsPDU *pdu, V9fsFidState *fidp,
+                                  struct timespec times[2])
+{
+    int err;
+    V9fsState *s = pdu->s;
+
+    if (v9fs_request_cancelled(pdu)) {
+        return -EINTR;
+    }
+    v9fs_co_run_in_worker(
+        {
+            err = s->ops->futimens(&s->ctx, fidp->fid_type, &fidp->fs, times);
+            if (err < 0) {
+                err = -errno;
+            }
+        });
+    return err;
+}
+
 int coroutine_fn v9fs_co_chown(V9fsPDU *pdu, V9fsPath *path, uid_t uid,
                                gid_t gid)
 {
@@ -184,6 +203,24 @@ int coroutine_fn v9fs_co_truncate(V9fsPDU *pdu, V9fsPath *path, off_t size)
     return err;
 }
 
+int coroutine_fn v9fs_co_ftruncate(V9fsPDU *pdu, V9fsFidState *fidp, off_t size)
+{
+    int err;
+    V9fsState *s = pdu->s;
+
+    if (v9fs_request_cancelled(pdu)) {
+        return -EINTR;
+    }
+    v9fs_co_run_in_worker(
+        {
+            err = s->ops->ftruncate(&s->ctx, fidp->fid_type, &fidp->fs, size);
+            if (err < 0) {
+                err = -errno;
+            }
+        });
+    return err;
+}
+
 int coroutine_fn v9fs_co_mknod(V9fsPDU *pdu, V9fsFidState *fidp,
                                V9fsString *name, uid_t uid, gid_t gid,
                                dev_t dev, mode_t mode, struct stat *stbuf)

hw/9pfs/coth.h

@@ -71,8 +71,12 @@ int coroutine_fn v9fs_co_statfs(V9fsPDU *, V9fsPath *, struct statfs *);
 int coroutine_fn v9fs_co_lstat(V9fsPDU *, V9fsPath *, struct stat *);
 int coroutine_fn v9fs_co_chmod(V9fsPDU *, V9fsPath *, mode_t);
 int coroutine_fn v9fs_co_utimensat(V9fsPDU *, V9fsPath *, struct timespec [2]);
+int coroutine_fn v9fs_co_futimens(V9fsPDU *pdu, V9fsFidState *fidp,
+                                  struct timespec times[2]);
 int coroutine_fn v9fs_co_chown(V9fsPDU *, V9fsPath *, uid_t, gid_t);
 int coroutine_fn v9fs_co_truncate(V9fsPDU *, V9fsPath *, off_t);
+int coroutine_fn v9fs_co_ftruncate(V9fsPDU *pdu, V9fsFidState *fidp,
+                                   off_t size);
 int coroutine_fn v9fs_co_llistxattr(V9fsPDU *, V9fsPath *, void *, size_t);
 int coroutine_fn v9fs_co_lgetxattr(V9fsPDU *, V9fsPath *,
                                    V9fsString *, void *, size_t);

tests/qtest/libqos/virtio-9p-client.c

@@ -557,6 +557,55 @@ void v9fs_rgetattr(P9Req *req, v9fs_attr *attr)
     v9fs_req_free(req);
 }
 
+/*
+ * size[4] Tsetattr tag[2] fid[4] valid[4] mode[4] uid[4] gid[4] size[8]
+ *                  atime_sec[8] atime_nsec[8] mtime_sec[8] mtime_nsec[8]
+ */
+TSetAttrRes v9fs_tsetattr(TSetAttrOpt opt)
+{
+    P9Req *req;
+    uint32_t err;
+
+    g_assert(opt.client);
+
+    req = v9fs_req_init(
+        opt.client, 4/*fid*/ + 4/*valid*/ + 4/*mode*/ + 4/*uid*/ + 4/*gid*/ +
+        8/*size*/ + 8/*atime_sec*/ + 8/*atime_nsec*/ + 8/*mtime_sec*/ +
+        8/*mtime_nsec*/, P9_TSETATTR, opt.tag
+    );
+    v9fs_uint32_write(req, opt.fid);
+    v9fs_uint32_write(req, (uint32_t) opt.attr.valid);
+    v9fs_uint32_write(req, opt.attr.mode);
+    v9fs_uint32_write(req, opt.attr.uid);
+    v9fs_uint32_write(req, opt.attr.gid);
+    v9fs_uint64_write(req, opt.attr.size);
+    v9fs_uint64_write(req, opt.attr.atime_sec);
+    v9fs_uint64_write(req, opt.attr.atime_nsec);
+    v9fs_uint64_write(req, opt.attr.mtime_sec);
+    v9fs_uint64_write(req, opt.attr.mtime_nsec);
+    v9fs_req_send(req);
+
+    if (!opt.requestOnly) {
+        v9fs_req_wait_for_reply(req, NULL);
+        if (opt.expectErr) {
+            v9fs_rlerror(req, &err);
+            g_assert_cmpint(err, ==, opt.expectErr);
+        } else {
+            v9fs_rsetattr(req);
+        }
+        req = NULL; /* request was freed */
+    }
+
+    return (TSetAttrRes) { .req = req };
+}
+
+/* size[4] Rsetattr tag[2] */
+void v9fs_rsetattr(P9Req *req)
+{
+    v9fs_req_recv(req, P9_RSETATTR);
+    v9fs_req_free(req);
+}
+
 /* size[4] Treaddir tag[2] fid[4] offset[8] count[4] */
 TReadDirRes v9fs_treaddir(TReadDirOpt opt)
 {

tests/qtest/libqos/virtio-9p-client.h

@@ -65,6 +65,16 @@ typedef struct v9fs_attr {
 #define P9_GETATTR_BASIC    0x000007ffULL /* Mask for fields up to BLOCKS */
 #define P9_GETATTR_ALL      0x00003fffULL /* Mask for ALL fields */
 
+#define P9_SETATTR_MODE         0x00000001UL
+#define P9_SETATTR_UID          0x00000002UL
+#define P9_SETATTR_GID          0x00000004UL
+#define P9_SETATTR_SIZE         0x00000008UL
+#define P9_SETATTR_ATIME        0x00000010UL
+#define P9_SETATTR_MTIME        0x00000020UL
+#define P9_SETATTR_CTIME        0x00000040UL
+#define P9_SETATTR_ATIME_SET    0x00000080UL
+#define P9_SETATTR_MTIME_SET    0x00000100UL
+
 struct V9fsDirent {
     v9fs_qid qid;
     uint64_t offset;
@@ -182,6 +192,28 @@ typedef struct TGetAttrRes {
     P9Req *req;
 } TGetAttrRes;
 
+/* options for 'Tsetattr' 9p request */
+typedef struct TSetAttrOpt {
+    /* 9P client being used (mandatory) */
+    QVirtio9P *client;
+    /* user supplied tag number being returned with response (optional) */
+    uint16_t tag;
+    /* file ID of file/dir whose attributes shall be modified (required) */
+    uint32_t fid;
+    /* new attribute values to be set by 9p server */
+    v9fs_attr attr;
+    /* only send Tsetattr request but not wait for a reply? (optional) */
+    bool requestOnly;
+    /* do we expect an Rlerror response, if yes which error code? (optional) */
+    uint32_t expectErr;
+} TSetAttrOpt;
+
+/* result of 'Tsetattr' 9p request */
+typedef struct TSetAttrRes {
+    /* if requestOnly was set: request object for further processing */
+    P9Req *req;
+} TSetAttrRes;
+
 /* options for 'Treaddir' 9p request */
 typedef struct TReadDirOpt {
     /* 9P client being used (mandatory) */
@@ -470,6 +502,8 @@ TWalkRes v9fs_twalk(TWalkOpt opt);
 void v9fs_rwalk(P9Req *req, uint16_t *nwqid, v9fs_qid **wqid);
 TGetAttrRes v9fs_tgetattr(TGetAttrOpt);
 void v9fs_rgetattr(P9Req *req, v9fs_attr *attr);
+TSetAttrRes v9fs_tsetattr(TSetAttrOpt opt);
+void v9fs_rsetattr(P9Req *req);
 TReadDirRes v9fs_treaddir(TReadDirOpt);
 void v9fs_rreaddir(P9Req *req, uint32_t *count, uint32_t *nentries,
                    struct V9fsDirent **entries);

tests/qtest/virtio-9p-test.c

@@ -20,6 +20,7 @@
 #define tversion(...) v9fs_tversion((TVersionOpt) __VA_ARGS__)
 #define tattach(...) v9fs_tattach((TAttachOpt) __VA_ARGS__)
 #define tgetattr(...) v9fs_tgetattr((TGetAttrOpt) __VA_ARGS__)
+#define tsetattr(...) v9fs_tsetattr((TSetAttrOpt) __VA_ARGS__)
 #define treaddir(...) v9fs_treaddir((TReadDirOpt) __VA_ARGS__)
 #define tlopen(...) v9fs_tlopen((TLOpenOpt) __VA_ARGS__)
 #define twrite(...) v9fs_twrite((TWriteOpt) __VA_ARGS__)
@@ -735,6 +736,20 @@ static void fs_use_after_unlink(void *obj, void *data,
         .data = buf
     }).count;
     g_assert_cmpint(count, ==, write_count);
+
+    /* truncate file to (arbitrarily chosen) size 2001 */
+    tsetattr({
+        .client = v9p, .fid = fid_file, .attr = (v9fs_attr) {
+            .valid = P9_SETATTR_SIZE,
+            .size = 2001
+        }
+     });
+    /* truncate apparently succeeded, let's double-check the size */
+    tgetattr({
+        .client = v9p, .fid = fid_file, .request_mask = P9_GETATTR_BASIC,
+        .rgetattr.attr = &attr
+    });
+    g_assert_cmpint(attr.size, ==, 2001);
 }
 
 static void cleanup_9p_local_driver(void *data)