[Minios-devel] [UNIKRAFT PATCH v4 13/22] lib/vfscore: introduce fget, fdrop, fdalloc

[Yuri Volchkov <yuri.volchkov@xxxxxxxxx>]

These functions are used in the imported code, which is not enabled
yet. This required to expand functionality of vfscore_install_fd and
friends with locking and reference counting.

Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
---
 lib/vfscore/fd.c                   | 71 ++++++++++++++++++++++++++++--
 lib/vfscore/file.c                 | 22 ++++++++-
 lib/vfscore/include/vfscore/file.h |  9 +++-
 3 files changed, 96 insertions(+), 6 deletions(-)

diff --git a/lib/vfscore/fd.c b/lib/vfscore/fd.c
index 6c220428..5abed969 100644
--- a/lib/vfscore/fd.c
+++ b/lib/vfscore/fd.c
@@ -74,20 +74,45 @@ exit:
 
 void vfscore_put_fd(int fd)
 {
+       struct vfscore_file *fp;
+       unsigned long flags;
+
        UK_ASSERT(fd < (int) FDTABLE_MAX_FILES);
        /* Currently it is not allowed to free std(in|out|err) */
        UK_ASSERT(fd > 2);
 
-       __uk_clear_bit(fd, &fdtable.bitmap);
+       flags = ukplat_lcpu_save_irqf();
+       __uk_clear_bit(fd, &fdtable.bitmap);\
+       fp = fdtable.files[fd];
+       fdtable.files[fd] = NULL;
+       ukplat_lcpu_restore_irqf(flags);
+
+       fdrop(fp);
 }
 
-void vfscore_install_fd(int fd, struct vfscore_file *file)
+int vfscore_install_fd(int fd, struct vfscore_file *file)
 {
-       UK_ASSERT(fd < (int) FDTABLE_MAX_FILES);
-       UK_ASSERT(file);
+       unsigned long flags;
+       struct vfscore_file *orig;
+
+       if ((fd >= (int) FDTABLE_MAX_FILES) || (!file))
+               return -EBADF;
+
+       fhold(file);
 
        file->fd = fd;
+
+       flags = ukplat_lcpu_save_irqf();
+       orig = fdtable.files[fd];
        fdtable.files[fd] = file;
+       ukplat_lcpu_restore_irqf(flags);
+
+       fdrop(file);
+
+       if (orig)
+               fdrop(orig);
+
+       return 0;
 }
 
 struct vfscore_file *vfscore_get_file(int fd)
@@ -101,12 +126,50 @@ struct vfscore_file *vfscore_get_file(int fd)
        if (!(fdtable.bitmap & ((uint64_t) 1 << fd)))
                goto exit;
        ret = fdtable.files[fd];
+       fhold(ret);
 
 exit:
        ukplat_lcpu_restore_irqf(flags);
        return ret;
 }
 
+int fget(int fd, struct vfscore_file **out_fp)
+{
+       int ret = 0;
+       struct vfscore_file *fp = vfscore_get_file(fd);
+
+       if (!fp)
+               ret = EBADF;
+       else
+               *out_fp = fp;
+
+       return ret;
+}
+
+int fdalloc(struct vfscore_file *fp, int *newfd)
+{
+       int fd, ret = 0;
+
+       fhold(fp);
+
+       fd = vfscore_alloc_fd();
+       if (fd < 0) {
+               ret = fd;
+               goto exit;
+       }
+
+       ret = vfscore_install_fd(fd, fp);
+       if (ret)
+               fdrop(fp);
+       else
+               *newfd = fd;
+
+exit:
+       return ret;
+}
+
+
+/* TODO: move this constructor to main.c */
 __constructor static void fdtable_init(void)
 {
        memset(&fdtable, 0, sizeof(fdtable));
diff --git a/lib/vfscore/file.c b/lib/vfscore/file.c
index e7adf1a3..0f6dfa93 100644
--- a/lib/vfscore/file.c
+++ b/lib/vfscore/file.c
@@ -38,7 +38,7 @@
 #include <uk/print.h>
 #include <vfscore/file.h>
 #include <uk/assert.h>
-
+#include <uk/arch/atomic.h>
 
 int close(int fd)
 {
@@ -95,3 +95,23 @@ ssize_t read(int fd, void *buf, size_t count)
 
        return file->fops->read(file, buf, count);
 }
+
+/* TODO: remove stub */
+#define vfs_close(fp) (0)
+
+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;
+}
+void fhold(struct vfscore_file *fp)
+{
+       ukarch_inc(&fp->f_count);
+}
diff --git a/lib/vfscore/include/vfscore/file.h 
b/lib/vfscore/include/vfscore/file.h
index 3d8d667f..84eb35d7 100644
--- a/lib/vfscore/include/vfscore/file.h
+++ b/lib/vfscore/include/vfscore/file.h
@@ -53,14 +53,21 @@ struct vfscore_fops {
 
 struct vfscore_file {
        int fd;
+       int             f_count;        /* reference count */
        const struct vfscore_fops *fops;
 };
 
 int vfscore_alloc_fd(void);
 void vfscore_put_fd(int fd);
-void vfscore_install_fd(int fd, struct vfscore_file *file);
+int vfscore_install_fd(int fd, struct vfscore_file *file);
 struct vfscore_file *vfscore_get_file(int fd);
 
+/*
+ * File descriptors reference count
+ */
+void fhold(struct vfscore_file* fp);
+int fdrop(struct vfscore_file* fp);
+
 #define FOF_OFFSET  0x0800    /* Use the offset in uio argument */
 
 #ifdef __cplusplus
-- 
2.19.2


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