威县做网站哪里好,wordpress首页文章图片不显示,重庆网站空间,百度登录1.swapon开启zram交换分区
swapon /dev/block/zram0
mkswap /dev/block/zram0
上面命令调用了linux的swapon系统调用启动zram0交换分区;mkswap命令向块设备文件/dev/block/zram0写入了swap_header信息
问题#xff1a;实际安卓平台是哪里触发swapon和mkswap调用的#xff…1.swapon开启zram交换分区
swapon /dev/block/zram0
mkswap /dev/block/zram0
上面命令调用了linux的swapon系统调用启动zram0交换分区;mkswap命令向块设备文件/dev/block/zram0写入了swap_header信息
问题实际安卓平台是哪里触发swapon和mkswap调用的我们已MTK8195平台为例
init.xxx.rc:swapon_all /vendor/etc/fstab.enableswap其中fstab.enableswap内容如下
/dev/block/zram0 none swap defaults zramsizexx% 那么swapon_all命令执行了哪里的代码呢又是哪里解析fstab.enableswap文件呢答案是
system/core/init/builtins.cpp /* swapon_all [ fstab ] */
static Resultvoid do_swapon_all(const BuiltinArguments args) {auto swapon_all ParseSwaponAll(args.args);if (!swapon_all.ok()) return swapon_all.error();Fstab fstab;if (swapon_all-empty()) {if (!ReadDefaultFstab(fstab)) {return Error() Could not read default fstab;}} else {if (!ReadFstabFromFile(*swapon_all, fstab)) {return Error() Could not read fstab *swapon_all ;}}if (!fs_mgr_swapon_all(fstab)) { return Error() fs_mgr_swapon_all() failed;}return {};
}
而fs_mgr_swapon_all实现/system/core/fs_mgr/fs_mgr.cpp
bool fs_mgr_swapon_all(const Fstab fstab) {...const char* mkswap_argv[2] {MKSWAP_BIN,entry.blk_device.c_str(),};int err logwrap_fork_execvp(ARRAY_SIZE(mkswap_argv), mkswap_argv, nullptr, false,LOG_KLOG, false, nullptr);if (err) {LERROR mkswap failed for entry.blk_device;ret false;continue;}/* If -1, then no priority was specified in fstab, so dont set* SWAP_FLAG_PREFER or encode the priority */int flags 0;if (entry.swap_prio 0) {flags (entry.swap_prio SWAP_FLAG_PRIO_SHIFT) SWAP_FLAG_PRIO_MASK;flags | SWAP_FLAG_PREFER;} else {flags 0;}err swapon(entry.blk_device.c_str(), flags);if (err) {LERROR swapon failed for entry.blk_device;ret false;}...
}
2.swapon系统调用
kernel-5.15/mm/swapfile.c
swapon(...) {swap_file file_open_name(name, O_RDWR|O_LARGEFILE, 0);p-swap_file swap_file;mapping swap_file-f_mapping;dentry swap_file-f_path.dentry;inode mapping-host;/** Read the swap header.*/if (!mapping-a_ops-readpage) {error -EINVAL;goto bad_swap_unlock_inode;}page read_mapping_page(mapping, 0, swap_file);if (IS_ERR(page)) {error PTR_ERR(page);goto bad_swap_unlock_inode;}swap_header kmap(page);maxpages read_swap_header(p, swap_header, inode);...nr_extents setup_swap_map_and_extents(p, swap_header, swap_map, cluster_info, maxpages, span);...error init_swap_address_space(p-type, maxpages);...
}上面代码read_mapping_page是能够读取内容的关键是mapping对象因为mapping-aops有readpage函数但是这里mapping和mapping-aops是什么时候设置的先公布答案mapping的aops指向的是def_blk_aops定义在kernel-5.15/block/fops.c:
const struct address_space_operations def_blk_aops { .set_page_dirty __set_page_dirty_buffers,.readpage blkdev_readpage,.readahead blkdev_readahead,.writepage blkdev_writepage,.write_begin blkdev_write_begin,.write_end blkdev_write_end,.writepages blkdev_writepages,.direct_IO blkdev_direct_IO,.migratepage buffer_migrate_page_norefs,.is_dirty_writeback buffer_check_dirty_writeback,
};
但是这是什么代码路径设置进去的呢我们就以zram为例一切要从blk_alloc_disk函数说起
zram_drv.c:
static int zram_add(void)
{struct zram *zram;int ret, device_id;zram kzalloc(sizeof(struct zram), GFP_KERNEL);if (!zram)return -ENOMEM;ret idr_alloc(zram_index_idr, zram, 0, 0, GFP_KERNEL);if (ret 0)goto out_free_dev;device_id ret;init_rwsem(zram-init_lock);
#ifdef CONFIG_ZRAM_WRITEBACKspin_lock_init(zram-wb_limit_lock);
#endif/* gendisk structure */zram-disk blk_alloc_disk(NUMA_NO_NODE);...
}__blk_alloc_disk(kernel-5.15/block/genhd.c)--__alloc_disk_node(kernel-5.15/block/genhd.c)---bdev_alloc(kernel-5.15/block/bdev.c)struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
{struct block_device *bdev;struct inode *inode;inode new_inode(blockdev_superblock);if (!inode)return NULL;inode-i_mode S_IFBLK;inode-i_rdev 0;inode-i_data.a_ops def_blk_aops;mapping_set_gfp_mask(inode-i_data, GFP_USER);bdev I_BDEV(inode);mutex_init(bdev-bd_fsfreeze_mutex);spin_lock_init(bdev-bd_size_lock);bdev-bd_partno partno;bdev-bd_inode inode;bdev-bd_stats alloc_percpu(struct disk_stats);if (!bdev-bd_stats) {iput(inode);return NULL;}bdev-bd_disk disk;return bdev;
}
看到bdev_alloc可以看到inode-i_data.a_ops def_blk_aops就是设置的地方了。同时这里还生成了block_device我们再看下block_device是怎么生成的这里的关键是上面的new_inode调用到了哪里答案kernel-5.15/fs/inode.c:new_inode函数
kernel-5.15/fs/inode.c:struct inode *new_inode(struct super_block *sb)
{struct inode *inode;spin_lock_prefetch(sb-s_inode_list_lock);inode new_inode_pseudo(sb);if (inode)inode_sb_list_add(inode);return inode;
}kernel-5.15/fs/inode.c:struct inode *new_inode_pseudo(struct super_block *sb)
{struct inode *inode alloc_inode(sb);if (inode) {spin_lock(inode-i_lock);inode-i_state 0;spin_unlock(inode-i_lock);INIT_LIST_HEAD(inode-i_sb_list);}return inode;
}kernel-5.15/fs/inode.c:static struct inode *alloc_inode(struct super_block *sb)
{const struct super_operations *ops sb-s_op;struct inode *inode;if (ops-alloc_inode)//调用对应的alloc_inode我们分析的场景调用到了kernel-5.15/block/bdev.c:bdev_alloc_inodeinode ops-alloc_inode(sb);elseinode kmem_cache_alloc(inode_cachep, GFP_KERNEL);if (!inode)return NULL;//很重要的初始化函数inode_init_alwaysif (unlikely(inode_init_always(sb, inode))) {if (ops-destroy_inode) {ops-destroy_inode(inode);if (!ops-free_inode)return NULL;}inode-free_inode ops-free_inode;i_callback(inode-i_rcu);return NULL;}return inode;
}
最终new_inode调用到了kernel-5.15/fs/inode.c:z的alloc_inode函数如下 static struct inode *bdev_alloc_inode(struct super_block *sb)
{struct bdev_inode *ei kmem_cache_alloc(bdev_cachep, GFP_KERNEL);if (!ei)return NULL;memset(ei-bdev, 0, sizeof(ei-bdev));return ei-vfs_inode;
}int inode_init_always(struct super_block *sb, struct inode *inode)
{static const struct inode_operations empty_iops;static const struct file_operations no_open_fops {.open no_open};struct address_space *const mapping inode-i_data;inode-i_sb sb;inode-i_blkbits sb-s_blocksize_bits;inode-i_flags 0;atomic64_set(inode-i_sequence, 0);atomic_set(inode-i_count, 1);inode-i_op empty_iops;inode-i_fop no_open_fops;inode-i_ino 0;inode-__i_nlink 1;inode-i_opflags 0;if (sb-s_xattr)inode-i_opflags | IOP_XATTR;i_uid_write(inode, 0);i_gid_write(inode, 0);atomic_set(inode-i_writecount, 0);inode-i_size 0;inode-i_write_hint WRITE_LIFE_NOT_SET;inode-i_blocks 0;inode-i_bytes 0;inode-i_generation 0;inode-i_pipe NULL;inode-i_cdev NULL;inode-i_link NULL;inode-i_dir_seq 0;inode-i_rdev 0;inode-dirtied_when 0;...mapping-a_ops empty_aops;mapping-host inode;
}
