[Qemu-devel] [PATCH -V2 2/6] hw/9pfs: Add file descriptor reclaim support

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 hw/9pfs/virtio-9p.c |   99 ++++++++++++++++++++++++++++++++++++++++++++++++--
 1 files changed, 95 insertions(+), 4 deletions(-)

diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index a9f52c6..811ac38 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -20,6 +20,7 @@
 #include "virtio-9p-xattr.h"
 
 int debug_9p_pdu;
+static void v9fs_reclaim_fd(V9fsState *s);
 
 enum {
     Oread   = 0x00,
@@ -107,7 +108,12 @@ static int v9fs_do_closedir(V9fsState *s, DIR *dir)
 
 static int v9fs_do_open(V9fsState *s, V9fsString *path, int flags)
 {
-    return s->ops->open(&s->ctx, path->data, flags);
+    int fd;
+    fd = s->ops->open(&s->ctx, path->data, flags);
+    if (fd > P9_FD_RECLAIM_THRES) {
+        v9fs_reclaim_fd(s);
+    }
+    return fd;
 }
 
 static DIR *v9fs_do_opendir(V9fsState *s, V9fsString *path)
@@ -188,6 +194,7 @@ static int v9fs_do_fstat(V9fsState *s, int fd, struct stat *stbuf)
 static int v9fs_do_open2(V9fsState *s, char *fullname, uid_t uid, gid_t gid,
         int flags, int mode)
 {
+    int fd;
     FsCred cred;
 
     cred_init(&cred);
@@ -196,7 +203,11 @@ static int v9fs_do_open2(V9fsState *s, char *fullname, uid_t uid, gid_t gid,
     cred.fc_mode = mode & 07777;
     flags = flags;
 
-    return s->ops->open2(&s->ctx, fullname, flags, &cred);
+    fd = s->ops->open2(&s->ctx, fullname, flags, &cred);
+    if (fd > P9_FD_RECLAIM_THRES) {
+        v9fs_reclaim_fd(s);
+    }
+    return fd;
 }
 
 static int v9fs_do_symlink(V9fsState *s, V9fsFidState *fidp,
@@ -434,6 +445,23 @@ static V9fsFidState *lookup_fid(V9fsState *s, int32_t fid)
 
     for (f = s->fid_list; f; f = f->next) {
         if (f->fid == fid) {
+            /*
+             * check whether we need to reopen the
+             * file. We might have closed the fd
+             * while trying to free up some file
+             * descriptors.
+             */
+            if (f->fsmap.fid_type == P9_FID_FILE) {
+                /* FIXME!! should we remember the open flags ?*/
+                if (f->fsmap.fs.fd == -1) {
+                    f->fsmap.fs.fd = v9fs_do_open(s, &f->fsmap.path, O_RDWR);
+                }
+            }
+            /*
+             * Mark the fid as referenced so that the LRU
+             * reclaim won't close the file descriptor
+             */
+            f->fsmap.flags |= FID_REFERENCED;
             return f;
         }
     }
@@ -461,6 +489,62 @@ static V9fsFidState *alloc_fid(V9fsState *s, int32_t fid)
     return f;
 }
 
+static void v9fs_reclaim_fd(V9fsState *s)
+{
+    int reclaim_count = 0;
+    V9fsFidState *f;
+
+    for (f = s->fid_list; f; f = f->next) {
+        /*
+         * Unlink fids cannot be reclaimed. Check
+         * for them and skip them
+         */
+        if (f->fsmap.flags & FID_NON_RECLAIMABLE) {
+            continue;
+        }
+        /*
+         * if it is a recently referenced fid
+         * we leave the fid untouched and clear the
+         * reference bit. We come back to it later
+         * in the next iteration. (a simple LRU without
+         * moving list elements around)
+         */
+        if (f->fsmap.flags & FID_REFERENCED) {
+            f->fsmap.flags  &= ~FID_REFERENCED;
+            continue;
+        }
+        /*
+         * reclaim fd, by closing the file descriptors
+         */
+        if (f->fsmap.fid_type == P9_FID_FILE) {
+            if (f->fsmap.fs.fd != -1) {
+                v9fs_do_close(s, f->fsmap.fs.fd);
+                f->fsmap.fs.fd = -1;
+                reclaim_count++;
+            }
+        }
+        if (reclaim_count >= P9_FD_RECLAIM_THRES/2) {
+            break;
+        }
+    }
+}
+
+static void v9fs_mark_fids_unreclaim(V9fsState *s, V9fsString *str)
+{
+    V9fsFidState *fidp;
+    for (fidp = s->fid_list; fidp; fidp = fidp->next) {
+        if (!strcmp(fidp->fsmap.path.data, str->data)) {
+            /* Mark the fid non reclaimable. */
+            fidp->fsmap.flags  |= FID_NON_RECLAIMABLE;
+            /* reopen the file if already closed */
+            if (fidp->fsmap.fs.fd == -1) {
+                fidp->fsmap.fs.fd = v9fs_do_open(s, &fidp->fsmap.path, O_RDWR);
+            }
+        }
+    }
+}
+
+
 static int v9fs_xattr_fid_clunk(V9fsState *s, V9fsFidState *fidp)
 {
     int retval = 0;
@@ -516,7 +600,10 @@ static int free_fid(V9fsState *s, int32_t fid)
     *fidpp = fidp->next;
 
     if (fidp->fsmap.fid_type == P9_FID_FILE) {
-        v9fs_do_close(s, fidp->fsmap.fs.fd);
+        /* I we reclaimed the fd no need to close */
+        if (fidp->fsmap.fs.fd != -1) {
+            v9fs_do_close(s, fidp->fsmap.fs.fd);
+        }
     } else if (fidp->fsmap.fid_type == P9_FID_DIR) {
         v9fs_do_closedir(s, fidp->fsmap.fs.dir);
     } else if (fidp->fsmap.fid_type == P9_FID_XATTR) {
@@ -2719,7 +2806,11 @@ static void v9fs_remove(V9fsState *s, V9fsPDU *pdu)
         err = -EINVAL;
         goto out;
     }
-
+    /*
+     * IF the file is unlinked, we cannot reopen
+     * the file later. So don't reclaim fd
+     */
+    v9fs_mark_fids_unreclaim(s, &vs->fidp->fsmap.path);
     err = v9fs_do_remove(s, &vs->fidp->fsmap.path);
     v9fs_remove_post_remove(s, vs, err);
     return;
-- 
1.7.1