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[PATCH 4/9] btrfs: Avoid a rescan for a device which was already not fou

From: Goffredo Baroncelli
Subject: [PATCH 4/9] btrfs: Avoid a rescan for a device which was already not found.
Date: Thu, 11 Oct 2018 20:50:58 +0200

From: Goffredo Baroncelli <address@hidden>

Currently read from missing device triggers rescan. However, it is never
recorded that the device is missing. So, each read of a missing device
triggers rescan again and again. This behavior causes a lot of unneeded
rescans leading to huge slowdowns.

This patch fixes above mentioned issue. Information about missing devices
is stored in the data->devices_attached[] array as NULL value in dev
member. Rescan is triggered only if no information is found for a given
device. This means that only first time read triggers rescan.

The patch drops premature return. This way data->devices_attached[] is
filled even when a given device is missing.

Signed-off-by: Goffredo Baroncelli <address@hidden>
 grub-core/fs/btrfs.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
index 2a87eb103..b2be80c33 100644
--- a/grub-core/fs/btrfs.c
+++ b/grub-core/fs/btrfs.c
@@ -588,7 +588,7 @@ find_device_iter (const char *name, void *data)
 static grub_device_t
-find_device (struct grub_btrfs_data *data, grub_uint64_t id, int do_rescan)
+find_device (struct grub_btrfs_data *data, grub_uint64_t id)
   struct find_device_ctx ctx = {
     .data = data,
@@ -600,10 +600,9 @@ find_device (struct grub_btrfs_data *data, grub_uint64_t 
id, int do_rescan)
   for (i = 0; i < data->n_devices_attached; i++)
     if (id == data->devices_attached[i].id)
       return data->devices_attached[i].dev;
-  if (do_rescan)
-    grub_device_iterate (find_device_iter, &ctx);
-  if (!ctx.dev_found)
-    return NULL;
+  grub_device_iterate (find_device_iter, &ctx);
   if (data->n_devices_attached > data->n_devices_allocated)
@@ -615,7 +614,8 @@ find_device (struct grub_btrfs_data *data, grub_uint64_t 
id, int do_rescan)
                        * sizeof (data->devices_attached[0]));
       if (!data->devices_attached)
-         grub_device_close (ctx.dev_found);
+         if (ctx.dev_found)
+           grub_device_close (ctx.dev_found);
          data->devices_attached = tmp;
          return NULL;
@@ -897,7 +897,7 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, 
grub_disk_addr_t addr,
                              " for laddr 0x%" PRIxGRUB_UINT64_T "\n", paddr,
-               dev = find_device (data, stripe->device_id, j);
+               dev = find_device (data, stripe->device_id);
                if (!dev)
                    grub_dprintf ("btrfs",
@@ -974,7 +974,8 @@ grub_btrfs_unmount (struct grub_btrfs_data *data)
   unsigned i;
   /* The device 0 is closed one layer upper.  */
   for (i = 1; i < data->n_devices_attached; i++)
-    grub_device_close (data->devices_attached[i].dev);
+    if (data->devices_attached[i].dev)
+        grub_device_close (data->devices_attached[i].dev);
   grub_free (data->devices_attached);
   grub_free (data->extent);
   grub_free (data);

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