[Minios-devel] [UNIKRAFT VFS PATCH 1/3] Fix dentry referecing and file closing

[Mihai Pogonaru <pogonarumihai@xxxxxxxxx>]

Increase the refcount of the dentry when opening a file
Decrease the refcount of the dentry and free the file on closing

Make fdrop return 0 if the file's refcount hit 0 or 1 otherwise.
This is the OSv behaviour and the return of an error from fdrop
is never checked.

Signed-off-by: Mihai Pogonaru <pogonarumihai@xxxxxxxxx>
---
 lib/vfscore/file.c     | 18 ++++++++++++++----
 lib/vfscore/fops.c     |  7 ++++---
 lib/vfscore/syscalls.c |  3 +++
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/lib/vfscore/file.c b/lib/vfscore/file.c
index e56f16dc..e7627e96 100644
--- a/lib/vfscore/file.c
+++ b/lib/vfscore/file.c
@@ -42,15 +42,25 @@
 
 int fdrop(struct vfscore_file *fp)
 {
-       int ret = 0;
        int prev = ukarch_dec(&fp->f_count);
 
        if (prev == 0)
                UK_CRASH("Unbalanced fhold/fdrop");
 
-       if (prev == 1)
-               ret = vfs_close(fp);
-       return ret;
+       if (prev == 1) {
+               /*
+                * we free the file even in case of an error
+                * so release the dentry too
+                */
+               if (vfs_close(fp) != 0)
+                       drele(fp->f_dentry);
+
+               free(fp);
+
+               return 1;
+       }
+
+       return 0;
 }
 void fhold(struct vfscore_file *fp)
 {
diff --git a/lib/vfscore/fops.c b/lib/vfscore/fops.c
index 8f5c2e1b..0cef2c12 100644
--- a/lib/vfscore/fops.c
+++ b/lib/vfscore/fops.c
@@ -53,9 +53,10 @@ int vfs_close(struct vfscore_file *fp)
        if (error)
                return error;
 
-       /* Dentry stays forever in the dentry cache. Unless the
-        * file/directory it refers to gets deleted/renamed */
+       /* Release the dentry */
+       drele(fp->f_dentry);
        fp->f_dentry = NULL;
+
        return 0;
 }
 
@@ -103,7 +104,7 @@ int vfs_write(struct vfscore_file *fp, struct uio *uio, int 
flags)
                ioflags |= IO_SYNC;
 
        if ((flags & FOF_OFFSET) == 0)
-               uio->uio_offset = fp->f_offset;
+               uio->uio_offset = fp->f_offset;
 
        error = VOP_WRITE(vp, uio, ioflags);
        if (!error) {
diff --git a/lib/vfscore/syscalls.c b/lib/vfscore/syscalls.c
index 385d90c0..f9666c4c 100644
--- a/lib/vfscore/syscalls.c
+++ b/lib/vfscore/syscalls.c
@@ -204,6 +204,8 @@ sys_open(char *path, int flags, mode_t mode, struct 
vfscore_file **fpp)
        }
        fp->f_flags = flags;
 
+       // OSv was using a intrusive_ptr which was increasing the refcount
+       dref(dp);
        // change to std::move once dp is a dentry_ref
        fp->f_dentry = dp;
        dp = NULL;
@@ -214,6 +216,7 @@ sys_open(char *path, int flags, mode_t mode, struct 
vfscore_file **fpp)
                // Note direct delete of fp instead of fdrop(fp). fp was never
                // returned so cannot be in use, and because it wasn't opened
                // it cannot be close()ed.
+               drele(fp->f_dentry);
                free(fp);
                return error;
        }
-- 
2.11.0


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