sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 315 insertions, 0 deletions

diff --git a/fs/efs/inode.c b/fs/efs/inode.c
new file mode 100644
index 000000000..4b132729e
--- /dev/null
+++ b/fs/efs/inode.c
@@ -0,0 +1,315 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * inode.c
+ *
+ * Copyright (c) 1999 Al Smith
+ *
+ * Portions derived from work (c) 1995,1996 Christian Vogelgsang,
+ *              and from work (c) 1998 Mike Shaver.
+ */
+
+#include <linux/buffer_head.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include "efs.h"
+#include <linux/efs_fs_sb.h>
+
+static int efs_read_folio(struct file *file, struct folio *folio)
+{
+	return block_read_full_folio(folio, efs_get_block);
+}
+
+static sector_t _efs_bmap(struct address_space *mapping, sector_t block)
+{
+	return generic_block_bmap(mapping,block,efs_get_block);
+}
+
+static const struct address_space_operations efs_aops = {
+	.read_folio = efs_read_folio,
+	.bmap = _efs_bmap
+};
+
+static inline void extent_copy(efs_extent *src, efs_extent *dst) {
+	/*
+	 * this is slightly evil. it doesn't just copy
+	 * efs_extent from src to dst, it also mangles
+	 * the bits so that dst ends up in cpu byte-order.
+	 */
+
+	dst->cooked.ex_magic  =  (unsigned int) src->raw[0];
+	dst->cooked.ex_bn     = ((unsigned int) src->raw[1] << 16) |
+				((unsigned int) src->raw[2] <<  8) |
+				((unsigned int) src->raw[3] <<  0);
+	dst->cooked.ex_length =  (unsigned int) src->raw[4];
+	dst->cooked.ex_offset = ((unsigned int) src->raw[5] << 16) |
+				((unsigned int) src->raw[6] <<  8) |
+				((unsigned int) src->raw[7] <<  0);
+	return;
+}
+
+struct inode *efs_iget(struct super_block *super, unsigned long ino)
+{
+	int i, inode_index;
+	dev_t device;
+	u32 rdev;
+	struct buffer_head *bh;
+	struct efs_sb_info    *sb = SUPER_INFO(super);
+	struct efs_inode_info *in;
+	efs_block_t block, offset;
+	struct efs_dinode *efs_inode;
+	struct inode *inode;
+
+	inode = iget_locked(super, ino);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+	if (!(inode_state_read_once(inode) & I_NEW))
+		return inode;
+
+	in = INODE_INFO(inode);
+
+	/*
+	** EFS layout:
+	**
+	** |   cylinder group    |   cylinder group    |   cylinder group ..etc
+	** |inodes|data          |inodes|data          |inodes|data       ..etc
+	**
+	** work out the inode block index, (considering initially that the
+	** inodes are stored as consecutive blocks). then work out the block
+	** number of that inode given the above layout, and finally the
+	** offset of the inode within that block.
+	*/
+
+	inode_index = inode->i_ino /
+		(EFS_BLOCKSIZE / sizeof(struct efs_dinode));
+
+	block = sb->fs_start + sb->first_block + 
+		(sb->group_size * (inode_index / sb->inode_blocks)) +
+		(inode_index % sb->inode_blocks);
+
+	offset = (inode->i_ino %
+			(EFS_BLOCKSIZE / sizeof(struct efs_dinode))) *
+		sizeof(struct efs_dinode);
+
+	bh = sb_bread(inode->i_sb, block);
+	if (!bh) {
+		pr_warn("%s() failed at block %d\n", __func__, block);
+		goto read_inode_error;
+	}
+
+	efs_inode = (struct efs_dinode *) (bh->b_data + offset);
+    
+	inode->i_mode  = be16_to_cpu(efs_inode->di_mode);
+	set_nlink(inode, be16_to_cpu(efs_inode->di_nlink));
+	i_uid_write(inode, (uid_t)be16_to_cpu(efs_inode->di_uid));
+	i_gid_write(inode, (gid_t)be16_to_cpu(efs_inode->di_gid));
+	inode->i_size  = be32_to_cpu(efs_inode->di_size);
+	inode_set_atime(inode, be32_to_cpu(efs_inode->di_atime), 0);
+	inode_set_mtime(inode, be32_to_cpu(efs_inode->di_mtime), 0);
+	inode_set_ctime(inode, be32_to_cpu(efs_inode->di_ctime), 0);
+
+	/* this is the number of blocks in the file */
+	if (inode->i_size == 0) {
+		inode->i_blocks = 0;
+	} else {
+		inode->i_blocks = ((inode->i_size - 1) >> EFS_BLOCKSIZE_BITS) + 1;
+	}
+
+	rdev = be16_to_cpu(efs_inode->di_u.di_dev.odev);
+	if (rdev == 0xffff) {
+		rdev = be32_to_cpu(efs_inode->di_u.di_dev.ndev);
+		if (sysv_major(rdev) > 0xfff)
+			device = 0;
+		else
+			device = MKDEV(sysv_major(rdev), sysv_minor(rdev));
+	} else
+		device = old_decode_dev(rdev);
+
+	/* get the number of extents for this object */
+	in->numextents = be16_to_cpu(efs_inode->di_numextents);
+	in->lastextent = 0;
+
+	/* copy the extents contained within the inode to memory */
+	for(i = 0; i < EFS_DIRECTEXTENTS; i++) {
+		extent_copy(&(efs_inode->di_u.di_extents[i]), &(in->extents[i]));
+		if (i < in->numextents && in->extents[i].cooked.ex_magic != 0) {
+			pr_warn("extent %d has bad magic number in inode %llu\n",
+				i, inode->i_ino);
+			brelse(bh);
+			goto read_inode_error;
+		}
+	}
+
+	brelse(bh);
+	pr_debug("efs_iget(): inode %llu, extents %d, mode %o\n",
+		 inode->i_ino, in->numextents, inode->i_mode);
+	switch (inode->i_mode & S_IFMT) {
+		case S_IFDIR: 
+			inode->i_op = &efs_dir_inode_operations; 
+			inode->i_fop = &efs_dir_operations; 
+			break;
+		case S_IFREG:
+			inode->i_fop = &generic_ro_fops;
+			inode->i_data.a_ops = &efs_aops;
+			break;
+		case S_IFLNK:
+			inode->i_op = &page_symlink_inode_operations;
+			inode_nohighmem(inode);
+			inode->i_data.a_ops = &efs_symlink_aops;
+			break;
+		case S_IFCHR:
+		case S_IFBLK:
+		case S_IFIFO:
+			init_special_inode(inode, inode->i_mode, device);
+			break;
+		default:
+			pr_warn("unsupported inode mode %o\n", inode->i_mode);
+			goto read_inode_error;
+			break;
+	}
+
+	unlock_new_inode(inode);
+	return inode;
+        
+read_inode_error:
+	pr_warn("failed to read inode %llu\n", inode->i_ino);
+	iget_failed(inode);
+	return ERR_PTR(-EIO);
+}
+
+static inline efs_block_t
+efs_extent_check(efs_extent *ptr, efs_block_t block, struct efs_sb_info *sb) {
+	efs_block_t start;
+	efs_block_t length;
+	efs_block_t offset;
+
+	/*
+	 * given an extent and a logical block within a file,
+	 * can this block be found within this extent ?
+	 */
+	start  = ptr->cooked.ex_bn;
+	length = ptr->cooked.ex_length;
+	offset = ptr->cooked.ex_offset;
+
+	if ((block >= offset) && (block < offset+length)) {
+		return(sb->fs_start + start + block - offset);
+	} else {
+		return 0;
+	}
+}
+
+efs_block_t efs_map_block(struct inode *inode, efs_block_t block) {
+	struct efs_sb_info    *sb = SUPER_INFO(inode->i_sb);
+	struct efs_inode_info *in = INODE_INFO(inode);
+	struct buffer_head    *bh = NULL;
+
+	int cur, last, first = 1;
+	int ibase, ioffset, dirext, direxts, indext, indexts;
+	efs_block_t iblock, result = 0, lastblock = 0;
+	efs_extent ext, *exts;
+
+	last = in->lastextent;
+
+	if (in->numextents <= EFS_DIRECTEXTENTS) {
+		/* first check the last extent we returned */
+		if ((result = efs_extent_check(&in->extents[last], block, sb)))
+			return result;
+    
+		/* if we only have one extent then nothing can be found */
+		if (in->numextents == 1) {
+			pr_err("%s() failed to map (1 extent)\n", __func__);
+			return 0;
+		}
+
+		direxts = in->numextents;
+
+		/*
+		 * check the stored extents in the inode
+		 * start with next extent and check forwards
+		 */
+		for(dirext = 1; dirext < direxts; dirext++) {
+			cur = (last + dirext) % in->numextents;
+			if ((result = efs_extent_check(&in->extents[cur], block, sb))) {
+				in->lastextent = cur;
+				return result;
+			}
+		}
+
+		pr_err("%s() failed to map block %u (dir)\n", __func__, block);
+		return 0;
+	}
+
+	pr_debug("%s(): indirect search for logical block %u\n",
+		 __func__, block);
+	direxts = in->extents[0].cooked.ex_offset;
+	indexts = in->numextents;
+
+	for(indext = 0; indext < indexts; indext++) {
+		cur = (last + indext) % indexts;
+
+		/*
+		 * work out which direct extent contains `cur'.
+		 *
+		 * also compute ibase: i.e. the number of the first
+		 * indirect extent contained within direct extent `cur'.
+		 *
+		 */
+		ibase = 0;
+		for(dirext = 0; cur < ibase && dirext < direxts; dirext++) {
+			ibase += in->extents[dirext].cooked.ex_length *
+				(EFS_BLOCKSIZE / sizeof(efs_extent));
+		}
+
+		if (dirext == direxts) {
+			/* should never happen */
+			pr_err("couldn't find direct extent for indirect extent %d (block %u)\n",
+			       cur, block);
+			if (bh) brelse(bh);
+			return 0;
+		}
+		
+		/* work out block number and offset of this indirect extent */
+		iblock = sb->fs_start + in->extents[dirext].cooked.ex_bn +
+			(cur - ibase) /
+			(EFS_BLOCKSIZE / sizeof(efs_extent));
+		ioffset = (cur - ibase) %
+			(EFS_BLOCKSIZE / sizeof(efs_extent));
+
+		if (first || lastblock != iblock) {
+			if (bh) brelse(bh);
+
+			bh = sb_bread(inode->i_sb, iblock);
+			if (!bh) {
+				pr_err("%s() failed at block %d\n",
+				       __func__, iblock);
+				return 0;
+			}
+			pr_debug("%s(): read indirect extent block %d\n",
+				 __func__, iblock);
+			first = 0;
+			lastblock = iblock;
+		}
+
+		exts = (efs_extent *) bh->b_data;
+
+		extent_copy(&(exts[ioffset]), &ext);
+
+		if (ext.cooked.ex_magic != 0) {
+			pr_err("extent %d has bad magic number in block %d\n",
+			       cur, iblock);
+			if (bh) brelse(bh);
+			return 0;
+		}
+
+		if ((result = efs_extent_check(&ext, block, sb))) {
+			if (bh) brelse(bh);
+			in->lastextent = cur;
+			return result;
+		}
+	}
+	if (bh) brelse(bh);
+	pr_err("%s() failed to map block %u (indir)\n", __func__, block);
+	return 0;
+}  
+
+MODULE_DESCRIPTION("Extent File System (efs)");
+MODULE_LICENSE("GPL");