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fat: Batched discard support for fat

PATCH Superseded Kyungmin Park 2 participants 6 messages Mar 18, 2011 – Mar 28, 2011

Subsystems (2)
VFS VFAT/FAT/msdos filesystem

v5 of 6 Superseded Latest is v6 →

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Kyungmin Park

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#0 lore raw

PATCH v5 1/1 fat: Batched discard support for fat

From: Kyungmin Park <[email protected]>

FAT supports batched discard as ext4.

Cited from Lukas words.
"The current solution is not ideal because of its bad performance impact. So basic idea to improve things is to avoid discarding every time some blocks are freed. and instead batching is together into bigger trims, which tends to be more effective."

You can find an information in detail at following URLs.
http://lwn.net/Articles/397538/
http://lwn.net/Articles/383933/

Clearify the meaning of "len" (Cited form Lukas mail)

Let the "O" be free (bytes, blocks, whatever), and "=" be used. Now, we have a filesystem like this.

OOOO==O===OO===OOOOO==O===O===OOOOOOO===
^ ^
0 40

This is how it supposed to wotk if you have called FITIRM with parameters:

start = 0
minlen = 2
len = 20

So you will go through (blocks, bytes...) 0 -> 20

OOOO==O===OO===OOOOO==O===O===OOOOOOO===
^ ^
0 20

So, you will call discard on extents:

0-3
You'll skip 6 because is smaller than minlen
10-11
15-19

instead of

0-3
10-11
15-19
30-36

Signed-off-by Kyungmin Park <[email protected]>

---
Changelog v5:
Exit when start cluster is grater than max cluster

Changelog v4:
Simplify the exit condition

Changelog v3:
Adjust the minlen from queue discard_granularity Use the corrent len usage
Changelog v2:
Use the given start and len as Lukas comments Check the queue supports discard feature
---

fs/fat/fat.h +1 -0
index f504089..08b53e1 100644
@@ -299,6 +299,7 @@ extern int fat_alloc_clusters(struct inode *inode, int *cluster,
 			      int nr_cluster);
 extern int fat_free_clusters(struct inode *inode, int cluster);
 extern int fat_count_free_clusters(struct super_block *sb);
+extern int fat_trim_fs(struct super_block *sb, struct fstrim_range *range);
 
 /* fat/file.c */
 extern long fat_generic_ioctl(struct file *filp, unsigned int cmd,
fs/fat/fatent.c +96 -5

122 lines not on this page · raw message

fs/fat/file.c +30 -0
index 7257752..9910aba 100644
@@ -125,6 +125,36 @@ long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return fat_ioctl_get_attributes(inode, user_attr);
 	case FAT_IOCTL_SET_ATTRIBUTES:
 		return fat_ioctl_set_attributes(filp, user_attr);
+	case FITRIM:
+	{
+		struct super_block *sb = inode->i_sb;
+		struct request_queue *q = bdev_get_queue(sb->s_bdev);
+		struct fstrim_range range;
+		int ret = 0;
+
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (!blk_queue_discard(q))
+			return -EOPNOTSUPP;
+
+		if (copy_from_user(&range, (struct fstrim_range *)arg,
+					sizeof(range)))
+			return -EFAULT;
+
+		range.minlen = max((unsigned int)range.minlen,
+					q->limits.discard_granularity);
+		ret = fat_trim_fs(sb, &range);
+		if (ret < 0)
+			return ret;
+
+		if (copy_to_user((struct fstrim_range *)arg, &range,
+					sizeof(range)))
+			return -EFAULT;
+
+		return 0;
+	}
+
 	default:
 		return -ENOTTY;	/* Inappropriate ioctl for device */
 	}
maintainer
#1 lore raw
Quoted 125 lines · Kyungmin Park

From: Kyungmin Park <[email protected]>

FAT supports batched discard as ext4.

Cited from Lukas words.
"The current solution is not ideal because of its bad performance impact. So basic idea to improve things is to avoid discarding every time some blocks are freed. and instead batching is together into bigger trims, which tends to be more effective."

You can find an information in detail at following URLs.
http://lwn.net/Articles/397538/
http://lwn.net/Articles/383933/

Clearify the meaning of "len" (Cited form Lukas mail)

Let the "O" be free (bytes, blocks, whatever), and "=" be used. Now, we have a filesystem like this.

OOOO==O===OO===OOOOO==O===O===OOOOOOO===
^ ^
0 40

This is how it supposed to wotk if you have called FITIRM with parameters:

start = 0
minlen = 2
len = 20

So you will go through (blocks, bytes...) 0 -> 20

OOOO==O===OO===OOOOO==O===O===OOOOOOO===
^ ^
0 20

So, you will call discard on extents:

0-3
You'll skip 6 because is smaller than minlen
10-11
15-19

instead of

0-3
10-11
15-19
30-36

Signed-off-by Kyungmin Park <[email protected]>

---
Changelog v5:
Exit when start cluster is grater than max cluster

Changelog v4:
Simplify the exit condition

Changelog v3:
Adjust the minlen from queue discard_granularity Use the corrent len usage
Changelog v2:
Use the given start and len as Lukas comments Check the queue supports discard feature
---

fs/fat/fat.h +1 -0
index f504089..08b53e1 100644
@@ -299,6 +299,7 @@ extern int fat_alloc_clusters(struct inode *inode, int *cluster,
 			      int nr_cluster);
 extern int fat_free_clusters(struct inode *inode, int cluster);
 extern int fat_count_free_clusters(struct super_block *sb);
+extern int fat_trim_fs(struct super_block *sb, struct fstrim_range *range);
 
 /* fat/file.c */
 extern long fat_generic_ioctl(struct file *filp, unsigned int cmd,
fs/fat/fatent.c +15 -5
index b47d2c9..cc89ea6 100644
@@ -1,6 +1,8 @@
 /*
  * Copyright (C) 2004, OGAWA Hirofumi
  * Released under GPL v2.
+ *
+ * Batched discard support by Kyungmin Park <[email protected]>
  */
 
 #include <linux/module.h>

@@ -541,6 +543,16 @@ out:
 	return err;
 }
 
+static int fat_issue_discard(struct super_block *sb, int cluster, int nr_clus)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+	sector_t block, nr_blocks;
+
+	block = fat_clus_to_blknr(sbi, cluster);
+	nr_blocks = nr_clus * sbi->sec_per_clus;
+	return sb_issue_discard(sb, block, nr_blocks, GFP_NOFS, 0);
+}
+
 int fat_free_clusters(struct inode *inode, int cluster)
 {
 	struct super_block *sb = inode->i_sb;

@@ -575,11 +587,7 @@ int fat_free_clusters(struct inode *inode, int cluster)
 			if (cluster != fatent.entry + 1) {
 				int nr_clus = fatent.entry - first_cl + 1;
 
-				sb_issue_discard(sb,
-					fat_clus_to_blknr(sbi, first_cl),
-					nr_clus * sbi->sec_per_clus,
-					GFP_NOFS, 0);
-
+				fat_issue_discard(sb, first_cl, nr_clus);
 				first_cl = cluster;
 			}
 		}

@@ -683,3 +691,86 @@ out:
 	unlock_fat(sbi);
 	return err;
 }
+
+int fat_trim_fs(struct super_block *sb, struct fstrim_range *range)

fs/fat/fatent.c out: · line 705

Quoted 10 lines
fs/fat/fatent.c +10 -0
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+	struct fatent_operations *ops = sbi->fatent_ops;
+	struct fat_entry fatent;
+	unsigned long reada_blocks, reada_mask, cur_block;
+	int err, free, count, entry;
+	int start, len, minlen, trimmed;
+
+	start = range->start >> sb->s_blocksize_bits;
+	start = start / sbi->sec_per_clus;

start is round-down, I think it's strange interface. E.g. user specified the range as "start=10 len=1024". So the range should be 10-1034, i.e. (assume cluster-size is 512) 512-1024, right?

fs/fat/fatent.c out: · line 707

Quoted 2 lines
fs/fat/fatent.c +2 -0
+	len = range->len >> sb->s_blocksize_bits;
+	len = len / sbi->sec_per_clus;

And the end cluster should be round_down(start+len), right? i.e. start=10 len=1014, the end should be 1024 not 512.

fs/fat/fatent.c out: · line 716

Quoted 9 lines
fs/fat/fatent.c +9 -0
+	minlen = range->minlen >> sb->s_blocksize_bits;
+	minlen = minlen / sbi->sec_per_clus;
+	trimmed = 0;
+	count = 0;
+	err = -EINVAL;
+
+	lock_fat(sbi);
+	if (sbi->free_clusters != -1 && sbi->free_clus_valid)
+		goto out;

free clusters count validation doesn't matter here. If you want to check free cluster count, you should check free_clusters==0 or not (after validation).

fs/fat/fatent.c out: · line 718

Quoted 2 lines
fs/fat/fatent.c +2 -0
+	if (start >= sbi->max_cluster)
+		goto out;

This check can be done outside lock. And don't we need to check other parameters from userland?

fs/fat/fatent.c out: · line 730

Quoted 2 lines
fs/fat/fatent.c +2 -0
+	if (start < FAT_START_ENT)
+		start = FAT_START_ENT;

Valid data cluster is 2 - max_cluster, but it should be mapped to 0 - (max_cluster - FAT_START_ENT). Otherwise this interface's abstraction is useless, right?

fs/fat/fatent.c out: · line 736

Quoted 5 lines
fs/fat/fatent.c +5 -0
+	fatent_set_entry(&fatent, start);
+
+	while (count < sbi->max_cluster) {
+		if (fatent.entry >= sbi->max_cluster)
+			fatent.entry = FAT_START_ENT;

Why do we cyclic this?

Quoted 25 lines
fs/fat/fatent.c +25 -0
+		/* readahead of fat blocks */
+		if ((cur_block & reada_mask) == 0) {
+			unsigned long rest = sbi->fat_length - cur_block;
+			fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
+		}
+		cur_block++;
+
+		err = fat_ent_read_block(sb, &fatent);
+		if (err)
+			goto out;
+
+		do {
+			if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
+				free++;
+				if (!entry)
+					entry = fatent.entry;
+			} else if (entry) {
+				if (free >= minlen) {
+					fat_issue_discard(sb, entry, free);
+					trimmed += free;
+				}
+				free = 0;
+				entry = 0;
+			}
+			count++;

fs/fat/fatent.c out: · line 771

Quoted 10 lines
fs/fat/fatent.c +10 -0
+			if (count >= len)
+				goto done;
+		} while (fat_ent_next(sbi, &fatent));
+	}
+done:
+	if (free >= minlen) {
+		fat_issue_discard(sb, entry, free);
+		trimmed += free;
+	}
+	range->len = (trimmed * sbi->sec_per_clus) << sb->s_blocksize_bits;

this doesn't need cast?

	range->len = (u64)(trimmed * sbi->sec_per_clus) << sb->s_blocksize_bits;
Quoted 19 lines
fs/fat/fatent.c +5 -0
+	fatent_brelse(&fatent);
+out:
+	unlock_fat(sbi);
+	return err;
+}
fs/fat/file.c +6 -0
index 7257752..9910aba 100644
@@ -125,6 +125,36 @@ long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return fat_ioctl_get_attributes(inode, user_attr);
 	case FAT_IOCTL_SET_ATTRIBUTES:
 		return fat_ioctl_set_attributes(filp, user_attr);
+	case FITRIM:
+	{
+		struct super_block *sb = inode->i_sb;
+		struct request_queue *q = bdev_get_queue(sb->s_bdev);
+		struct fstrim_range range;
+		int ret = 0;

fs/fat/file.c long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) · line 143

Quoted 10 lines
fs/fat/file.c +10 -0
+
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (!blk_queue_discard(q))
+			return -EOPNOTSUPP;
+
+		if (copy_from_user(&range, (struct fstrim_range *)arg,
+					sizeof(range)))
+			return -EFAULT;

Please use __user annotation.

fs/fat/file.c long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) · line 146

Quoted 2 lines
fs/fat/file.c +2 -0
+		range.minlen = max((unsigned int)range.minlen,
+					q->limits.discard_granularity);

Please use max_t() instead.

Quoted 4 lines
fs/fat/file.c +4 -0
+		ret = fat_trim_fs(sb, &range);
+		if (ret < 0)
+			return ret;
+

fs/fat/file.c long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) · line 160

Quoted 10 lines
fs/fat/file.c +7 -0
+		if (copy_to_user((struct fstrim_range *)arg, &range,
+					sizeof(range)))
+			return -EFAULT;
+
+		return 0;
+	}
+
 	default:
 		return -ENOTTY;	/* Inappropriate ioctl for device */
 	}

This doesn't need compat_ioctl?

Thanks.

Signature · 1 line
OGAWA Hirofumi <[email protected]>
author
#2 lore raw
Quoted 133 lines · OGAWA Hirofumi
Quoted 131 lines · Kyungmin Park

From: Kyungmin Park <[email protected]>

FAT supports batched discard as ext4.

Cited from Lukas words.
"The current solution is not ideal because of its bad performance impact. So basic idea to improve things is to avoid discarding every time some blocks are freed. and instead batching is together into bigger trims, which tends to be more effective."

You can find an information in detail at following URLs.
http://lwn.net/Articles/397538/
http://lwn.net/Articles/383933/

Clearify the meaning of "len" (Cited form Lukas mail)

Let the "O" be free (bytes, blocks, whatever), and "=" be used. Now, we have a filesystem like this.

  OOOO==O===OO===OOOOO==O===O===OOOOOOO===
  ^                                      ^
  0                                      40

This is how it supposed to wotk if you have called FITIRM with parameters:

start = 0
minlen = 2
len = 20

So you will go through (blocks, bytes...) 0 -> 20

  OOOO==O===OO===OOOOO==O===O===OOOOOOO===
  ^                   ^
  0                   20

So, you will call discard on extents:

0-3
You'll skip 6 because is smaller than minlen
10-11
15-19

instead of

0-3
10-11
15-19
30-36

Signed-off-by Kyungmin Park <[email protected]>

---
Changelog v5:
      Exit when start cluster is grater than max cluster

Changelog v4:
      Simplify the exit condition

Changelog v3:
      Adjust the minlen from queue discard_granularity Use the corrent len usage
Changelog v2:
      Use the given start and len as Lukas comments Check the queue supports discard feature
---

fs/fat/fat.h +1 -0
index f504089..08b53e1 100644
@@ -299,6 +299,7 @@ extern int fat_alloc_clusters(struct inode *inode, int *cluster,
                             int nr_cluster);
  extern int fat_free_clusters(struct inode *inode, int cluster);
  extern int fat_count_free_clusters(struct super_block *sb);
+extern int fat_trim_fs(struct super_block *sb, struct fstrim_range *range);
 
  /* fat/file.c */
  extern long fat_generic_ioctl(struct file *filp, unsigned int cmd,
fs/fat/fatent.c +21 -5
index b47d2c9..cc89ea6 100644
@@ -1,6 +1,8 @@
  /*
   * Copyright (C) 2004, OGAWA Hirofumi
   * Released under GPL v2.
+ *
+ * Batched discard support by Kyungmin Park <[email protected]>
   */
 
  #include <linux/module.h>

@@ -541,6 +543,16 @@ out:
       return err;
  }
 
+static int fat_issue_discard(struct super_block *sb, int cluster, int nr_clus)
+{
+     struct msdos_sb_info *sbi = MSDOS_SB(sb);
+     sector_t block, nr_blocks;
+
+     block = fat_clus_to_blknr(sbi, cluster);
+     nr_blocks = nr_clus * sbi->sec_per_clus;
+     return sb_issue_discard(sb, block, nr_blocks, GFP_NOFS, 0);
+}
+
  int fat_free_clusters(struct inode *inode, int cluster)
  {
       struct super_block *sb = inode->i_sb;

@@ -575,11 +587,7 @@ int fat_free_clusters(struct inode *inode, int cluster)
                       if (cluster != fatent.entry + 1) {
                               int nr_clus = fatent.entry - first_cl + 1;
 
-                             sb_issue_discard(sb,
-                                     fat_clus_to_blknr(sbi, first_cl),
-                                     nr_clus * sbi->sec_per_clus,
-                                     GFP_NOFS, 0);
-
+                             fat_issue_discard(sb, first_cl, nr_clus);
                               first_cl = cluster;
                       }
               }

@@ -683,3 +691,86 @@ out:
       unlock_fat(sbi);
       return err;
  }
+
+int fat_trim_fs(struct super_block *sb, struct fstrim_range *range)
+{
+     struct msdos_sb_info *sbi = MSDOS_SB(sb);
+     struct fatent_operations *ops = sbi->fatent_ops;
+     struct fat_entry fatent;
+     unsigned long reada_blocks, reada_mask, cur_block;
+     int err, free, count, entry;
Quoted 8 lines

fs/fat/fatent.c out: · line 705

Quoted 4 lines
fs/fat/fatent.c +4 -0
+     int start, len, minlen, trimmed;
+
+     start = range->start >> sb->s_blocksize_bits;
+     start = start / sbi->sec_per_clus;

start is round-down, I think it's strange interface. E.g. user specified the range as "start=10 len=1024". So the range should be 10-1034, i.e. (assume cluster-size is 512) 512-1024, right?

I don't know what's the correct way? If you're right. it's better to round-up. If cluster-size is 32KiB and start sector is in the middle of cluster, then which is better. round-down or round-up?

Quoted 6 lines

fs/fat/fatent.c out: · line 707

Quoted 3 lines
fs/fat/fatent.c +2 -0
+     len = range->len >> sb->s_blocksize_bits;
+     len = len / sbi->sec_per_clus;

And the end cluster should be round_down(start+len), right? i.e. start=10 len=1014, the end should be 1024 not 512.

will fix it.

Quoted 11 lines

fs/fat/fatent.c out: · line 716

Quoted 10 lines
fs/fat/fatent.c +9 -0
+     minlen = range->minlen >> sb->s_blocksize_bits;
+     minlen = minlen / sbi->sec_per_clus;
+     trimmed = 0;
+     count = 0;
+     err = -EINVAL;
+
+     lock_fat(sbi);
+     if (sbi->free_clusters != -1 && sbi->free_clus_valid)
+             goto out;
Quoted 3 lines

free clusters count validation doesn't matter here. If you want to check free cluster count, you should check free_clusters==0 or not (after validation).

I borrowed it from "fat_count_free_clusters()". anyway fill fix it.

Quoted 6 lines

fs/fat/fatent.c out: · line 718

Quoted 3 lines
fs/fat/fatent.c +2 -0
+     if (start >= sbi->max_cluster)
+             goto out;

This check can be done outside lock. And don't we need to check other parameters from userland?

I refereed it from ext4. it checked at ext4 codes.

Quoted 7 lines

fs/fat/fatent.c out: · line 730

Quoted 3 lines
fs/fat/fatent.c +2 -0
+     if (start < FAT_START_ENT)
+             start = FAT_START_ENT;

Valid data cluster is 2 - max_cluster, but it should be mapped to 0 - (max_cluster - FAT_START_ENT). Otherwise this interface's abstraction is useless, right?

user program don't know the filesystem internals. The same program is used for ext4 and fat. so it should be handled at filesystem.

Quoted 8 lines

fs/fat/fatent.c out: · line 736

Quoted 6 lines
fs/fat/fatent.c +5 -0
+     fatent_set_entry(&fatent, start);
+
+     while (count < sbi->max_cluster) {
+             if (fatent.entry >= sbi->max_cluster)
+                     fatent.entry = FAT_START_ENT;

Why do we cyclic this?

If the start is middle and len is the whole disk size, then check the all clusters.

Quoted 39 lines
Quoted 26 lines
fs/fat/fatent.c +25 -0
+             /* readahead of fat blocks */
+             if ((cur_block & reada_mask) == 0) {
+                     unsigned long rest = sbi->fat_length - cur_block;
+                     fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
+             }
+             cur_block++;
+
+             err = fat_ent_read_block(sb, &fatent);
+             if (err)
+                     goto out;
+
+             do {
+                     if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
+                             free++;
+                             if (!entry)
+                                     entry = fatent.entry;
+                     } else if (entry) {
+                             if (free >= minlen) {
+                                     fat_issue_discard(sb, entry, free);
+                                     trimmed += free;
+                             }
+                             free = 0;
+                             entry = 0;
+                     }
+                     count++;

fs/fat/fatent.c out: · line 771

Quoted 10 lines
fs/fat/fatent.c +10 -0
+                     if (count >= len)
+                             goto done;
+             } while (fat_ent_next(sbi, &fatent));
+     }
+done:
+     if (free >= minlen) {
+             fat_issue_discard(sb, entry, free);
+             trimmed += free;
+     }
+     range->len = (trimmed * sbi->sec_per_clus) << sb->s_blocksize_bits;

this doesn't need cast?

Quoted 1 line

       range->len = (u64)(trimmed * sbi->sec_per_clus) << sb->s_blocksize_bits;

will fix it.

Quoted 24 lines
Quoted 24 lines
fs/fat/fatent.c +5 -0
+     fatent_brelse(&fatent);
+out:
+     unlock_fat(sbi);
+     return err;
+}
fs/fat/file.c +0 -0
index 7257752..9910aba 100644
@@ -125,6 +125,36 @@ long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
               return fat_ioctl_get_attributes(inode, user_attr);

      case FAT_IOCTL_SET_ATTRIBUTES:
              return fat_ioctl_set_attributes(filp, user_attr);
+     case FITRIM:
+     {
+             struct super_block *sb = inode->i_sb;
+             struct request_queue *q = bdev_get_queue(sb->s_bdev);
+             struct fstrim_range range;
+             int ret = 0;

fs/fat/file.c +4 -0
+
+             if (!capable(CAP_SYS_ADMIN))
+                     return -EPERM;
+
Quoted 8 lines
Quoted 6 lines

+             if (!blk_queue_discard(q))
+                     return -EOPNOTSUPP;
+
+             if (copy_from_user(&range, (struct fstrim_range *)arg,
+                                     sizeof(range)))
+                     return -EFAULT;

Please use __user annotation.

Okay

Quoted 5 lines
Quoted 3 lines

+             range.minlen = max((unsigned int)range.minlen,
+                                     q->limits.discard_granularity);

Please use max_t() instead.

Okay

Quoted 17 lines
Quoted 12 lines

+             ret = fat_trim_fs(sb, &range);
+             if (ret < 0)
+                     return ret;

fs/fat/file.c +8 -0
+
+             if (copy_to_user((struct fstrim_range *)arg, &range,
+                                     sizeof(range)))
+                     return -EFAULT;
+
+             return 0;
+     }
+
Quoted 3 lines

      default:
              return -ENOTTY; /* Inappropriate ioctl for device */ }

This doesn't need compat_ioctl?

I'm not sure it's needed?
I don't see other filesystem does.

Thank you,
Kyungmin Park

Quoted 10 lines

Thanks.
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OGAWA Hirofumi <[email protected]>
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maintainer
#3 lore raw
Quoted 10 lines · Kyungmin Park
Quoted 6 lines
Quoted 2 lines

+     start = range->start >> sb->s_blocksize_bits;
+     start = start / sbi->sec_per_clus;

start is round-down, I think it's strange interface. E.g. user specified the range as "start=10 len=1024". So the range should be 10-1034, i.e. (assume cluster-size is 512) 512-1024, right?

I don't know what's the correct way? If you're right. it's better to round-up. If cluster-size is 32KiB and start sector is in the middle of cluster, then which is better. round-down or round-up?

It depends on the design of this interface though, I bet it's round-up, and should use same way with other FSes.

Quoted 10 lines
Quoted 10 lines
Quoted 9 lines

+     minlen = range->minlen >> sb->s_blocksize_bits;
+     minlen = minlen / sbi->sec_per_clus;
+     trimmed = 0;
+     count = 0;
+     err = -EINVAL;
+
+     lock_fat(sbi);
+     if (sbi->free_clusters != -1 && sbi->free_clus_valid)
+             goto out;

Quoted 5 lines
Quoted 3 lines

free clusters count validation doesn't matter here. If you want to check free cluster count, you should check free_clusters==0 or not (after validation).

I borrowed it from "fat_count_free_clusters()". anyway fill fix it.

Yes. fat_count_free_clusters() needs to check free_clusters value, because it updates free_clusters value. If it's uptodate, does nothing.

Quoted 9 lines
Quoted 6 lines
Quoted 2 lines

+     if (start < FAT_START_ENT)
+             start = FAT_START_ENT;

Valid data cluster is 2 - max_cluster, but it should be mapped to 0 - (max_cluster - FAT_START_ENT). Otherwise this interface's abstraction is useless, right?

user program don't know the filesystem internals. The same program is used for ext4 and fat. so it should be handled at filesystem.

Yes. It's what I'm saying. If user wants to trim 0-2 then user will specify 0-2, but this trims only 2. It's not right.

Quoted 9 lines
Quoted 7 lines
Quoted 5 lines

+     fatent_set_entry(&fatent, start);
+
+     while (count < sbi->max_cluster) {
+             if (fatent.entry >= sbi->max_cluster)
+                     fatent.entry = FAT_START_ENT;

Why do we cyclic this?

If the start is middle and len is the whole disk size, then check the all clusters.

Strange design. If user wants to trim between middle and end, user have to know length from middle correctly? Ext4 really does it?

Thanks.

Signature · 5 lines
OGAWA Hirofumi <[email protected]>
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author
#4 lore raw
Quoted 42 lines · OGAWA Hirofumi
Quoted 10 lines · Kyungmin Park
Quoted 6 lines
Quoted 2 lines

+     start = range->start >> sb->s_blocksize_bits;
+     start = start / sbi->sec_per_clus;

start is round-down, I think it's strange interface. E.g. user specified the range as "start=10 len=1024". So the range should be 10-1034, i.e. (assume cluster-size is 512) 512-1024, right?

I don't know what's the correct way? If you're right. it's better to round-up. If cluster-size is 32KiB and start sector is in the middle of cluster, then which is better. round-down or round-up?

It depends on the design of this interface though, I bet it's round-up, and should use same way with other FSes.

Quoted 10 lines
Quoted 10 lines
Quoted 9 lines

+     minlen = range->minlen >> sb->s_blocksize_bits;
+     minlen = minlen / sbi->sec_per_clus;
+     trimmed = 0;
+     count = 0;
+     err = -EINVAL;
+
+     lock_fat(sbi);
+     if (sbi->free_clusters != -1 && sbi->free_clus_valid)
+             goto out;

Quoted 5 lines
Quoted 3 lines

free clusters count validation doesn't matter here. If you want to check free cluster count, you should check free_clusters==0 or not (after validation).

I borrowed it from "fat_count_free_clusters()". anyway fill fix it.

Yes. fat_count_free_clusters() needs to check free_clusters value, because it updates free_clusters value. If it's uptodate, does nothing.

Quoted 7 lines
Quoted 6 lines
Quoted 2 lines

+     if (start < FAT_START_ENT)
+             start = FAT_START_ENT;

Valid data cluster is 2 - max_cluster, but it should be mapped to 0 - (max_cluster - FAT_START_ENT). Otherwise this interface's abstraction is useless, right?

Quoted 5 lines
Quoted 2 lines

user program don't know the filesystem internals. The same program is used for ext4 and fat. so it should be handled at filesystem.

Yes. It's what I'm saying. If user wants to trim 0-2 then user will specify 0-2, but this trims only 2. It's not right.

There's similar code at ext4. it adjusts the start and len value if given start is less than first_data_blk.

       if (start < first_data_blk) {
                len -= first_data_blk - start;
                start = first_data_blk;
        }
Quoted 7 lines
Quoted 7 lines
Quoted 7 lines
Quoted 6 lines

+     fatent_set_entry(&fatent, start);
+
+     while (count < sbi->max_cluster) {
+             if (fatent.entry >= sbi->max_cluster)
+                     fatent.entry = FAT_START_ENT;

Quoted 6 lines
Quoted 3 lines
Quoted 1 line

Why do we cyclic this?

If the start is middle and len is the whole disk size, then check the all clusters.

Strange design. If user wants to trim between middle and end, user have to know length from middle correctly? Ext4 really does it?

You're right, it only check the one-direction. else return -EINVAL.

if (first_group > last_group)
return -EINVAL;

Quoted 5 lines

Thanks.
--
OGAWA Hirofumi <[email protected]>

maintainer
#5 lore raw
Quoted 10 lines · Kyungmin Park
Quoted 2 lines

Yes. It's what I'm saying. If user wants to trim 0-2 then user will specify 0-2, but this trims only 2. It's not right.

There's similar code at ext4. it adjusts the start and len value if given start is less than first_data_blk.

       if (start < first_data_blk) {
                len -= first_data_blk - start;
                start = first_data_blk;
        }

Oh, strange design. On this design, user have to know which block is actually start block per FSes (Yeah, you can still use this without start block knowledge. But it's bogus). I think it should fix ext4. No?

Thanks.

Signature · 1 line
OGAWA Hirofumi <[email protected]>