以下是关于zfs和zpool的伪原创内容，保持了原文的结构和大意，同时进行了改写：
// 创建一个zpool $ modprobe zfs $ zpool create -f -m /sample sample -o ashift=12 /dev/sdc $ zfs create sample/fs1 \ -o mountpoint=/sample/fs1 \ -o atime=off \ -o canmount=on \ -o compression=lz4 \ -o quota=100G \ -o recordsize=8k \ -o logbias=throughput// 手动卸载和挂载 $ umount /sample/fs1 $ zfs mount sample/fs1
zpool和zfs参数获取：
// 获取zfs pool的默认参数 $ zpool get all// 获取zfs pool挂载文件系统的参数 $ zfs get all
zfs和内核之间的桥梁super_operations：
const struct super_operations zpl_super_operations = {
.alloc_inode = zpl_inode_alloc,
.destroy_inode = zpl_inode_destroy,
.dirty_inode = zpl_dirty_inode,
.write_inode = NULL,
.evict_inode = zpl_evict_inode,
.put_super = zpl_put_super,
.sync_fs = zpl_sync_fs,
.statfs = zpl_statfs,
.remount_fs = zpl_remount_fs,
.show_devname = zpl_show_devname,
.show_options = zpl_show_options,
.show_stats = NULL,
};struct file_system_type zpl_fs_type = {
.owner = THIS_MODULE,
.name = ZFS_DRIVER,
.mount = zpl_mount,
.kill_sb = zpl_kill_sb,
};
inode_operations：
extern const struct inode_operations zpl_inode_operations; extern const struct inode_operations zpl_dir_inode_operations; extern const struct inode_operations zpl_symlink_inode_operations; extern const struct inode_operations zpl_special_inode_operations; extern dentry_operations_t zpl_dentry_operations; extern const struct address_space_operations zpl_address_space_operations; extern const struct file_operations zpl_file_operations; extern const struct file_operations zpl_dir_file_operations;/ zpl_super.c / extern void zpl_prune_sb(int64_t nr_to_scan, void *arg); extern const struct super_operations zpl_super_operations; extern const struct export_operations zpl_export_operations; extern struct file_system_type zpl_fs_type;
const struct inode_operations zpl_inode_operations = { .setattr = zpl_setattr, .getattr = zpl_getattr,
ifdef HAVE_GENERIC_SETXATTR
.setxattr = generic_setxattr, .getxattr = generic_getxattr, .removexattr = generic_removexattr,endif
.listxattr = zpl_xattr_list,if defined(CONFIG_FS_POSIX_ACL)
if defined(HAVE_SET_ACL)
.set_acl = zpl_set_acl,endif / HAVE_SET_ACL /
.get_acl = zpl_get_acl,endif / CONFIG_FS_POSIX_ACL /
};
const struct inode_operations zpl_dir_inode_operations = { .create = zpl_create, .lookup = zpl_lookup, .link = zpl_link, .unlink = zpl_unlink, .symlink = zpl_symlink, .mkdir = zpl_mkdir, .rmdir = zpl_rmdir, .mknod = zpl_mknod,
if defined(HAVE_RENAME_WANTS_FLAGS) || defined(HAVE_IOPS_RENAME_USERNS)
.rename = zpl_rename2,else
.rename = zpl_rename,endif
ifdef HAVE_TMPFILE
.tmpfile = zpl_tmpfile,endif
.setattr = zpl_setattr, .getattr = zpl_getattr,ifdef HAVE_GENERIC_SETXATTR
.setxattr = generic_setxattr, .getxattr = generic_getxattr, .removexattr = generic_removexattr,endif
.listxattr = zpl_xattr_list,if defined(CONFIG_FS_POSIX_ACL)
if defined(HAVE_SET_ACL)
.set_acl = zpl_set_acl,endif / HAVE_SET_ACL /
.get_acl = zpl_get_acl,endif / CONFIG_FS_POSIX_ACL /
};
const struct inode_operations zpl_symlink_inode_operations = {
ifdef HAVE_GENERIC_READLINK
.readlink = generic_readlink,endif
if defined(HAVE_GET_LINK_DELAYED) || defined(HAVE_GET_LINK_COOKIE)
.get_link = zpl_get_link,elif defined(HAVE_FOLLOW_LINK_COOKIE) || defined(HAVE_FOLLOW_LINK_NAMEIDATA)
.follow_link = zpl_follow_link,endif
if defined(HAVE_PUT_LINK_COOKIE) || defined(HAVE_PUT_LINK_NAMEIDATA)
.put_link = zpl_put_link,endif
.setattr = zpl_setattr, .getattr = zpl_getattr,ifdef HAVE_GENERIC_SETXATTR
.setxattr = generic_setxattr, .getxattr = generic_getxattr, .removexattr = generic_removexattr,endif
.listxattr = zpl_xattr_list,};
const struct inode_operations zpl_special_inode_operations = { .setattr = zpl_setattr, .getattr = zpl_getattr,
ifdef HAVE_GENERIC_SETXATTR
.setxattr = generic_setxattr, .getxattr = generic_getxattr, .removexattr = generic_removexattr,endif
.listxattr = zpl_xattr_list,if defined(CONFIG_FS_POSIX_ACL)
if defined(HAVE_SET_ACL)
.set_acl = zpl_set_acl,endif / HAVE_SET_ACL /
.get_acl = zpl_get_acl,endif / CONFIG_FS_POSIX_ACL /
};
dentry_operations_t zpl_dentry_operations = { .d_revalidate = zpl_revalidate, };
file_operations：
extern const struct inode_operations zpl_inode_operations; extern const struct inode_operations zpl_dir_inode_operations; extern const struct inode_operations zpl_symlink_inode_operations; extern const struct inode_operations zpl_special_inode_operations; extern dentry_operations_t zpl_dentry_operations; extern const struct address_space_operations zpl_address_space_operations; extern const struct file_operations zpl_file_operations; extern const struct file_operations zpl_dir_file_operations;const struct address_space_operations zpl_address_space_operations = { .readpages = zpl_readpages, .readpage = zpl_readpage, .writepage = zpl_writepage, .writepages = zpl_writepages, .direct_IO = zpl_direct_IO, };
const struct file_operations zpl_file_operations = { .open = zpl_open, .release = zpl_release, .llseek = zpl_llseek,
ifdef HAVE_VFS_RW_ITERATE
ifdef HAVE_NEW_SYNC_READ
.read = new_sync_read, .write = new_sync_write,endif
.read_iter = zpl_iter_read, .write_iter = zpl_iter_write,ifdef HAVE_VFS_IOV_ITER
.splice_read = generic_file_splice_read, .splice_write = iter_file_splice_write,endif
else
.read = do_sync_read, .write = do_sync_write, .aio_read = zpl_aio_read, .aio_write = zpl_aio_write,endif
.mmap = zpl_mmap, .fsync = zpl_fsync,ifdef HAVE_FILE_AIO_FSYNC
.aio_fsync = zpl_aio_fsync,endif
.fallocate = zpl_fallocate, .unlocked_ioctl = zpl_ioctl,ifdef CONFIG_COMPAT
.compat_ioctl = zpl_compat_ioctl,endif
};
const struct file_operations zpl_dir_file_operations = { .llseek = generic_file_llseek, .read = generic_read_dir,
if defined(HAVE_VFS_ITERATE_SHARED)
.iterate_shared = zpl_iterate,elif defined(HAVE_VFS_ITERATE)
.iterate = zpl_iterate,else
.readdir = zpl_readdir,endif
.fsync = zpl_fsync, .unlocked_ioctl = zpl_ioctl,ifdef CONFIG_COMPAT
.compat_ioctl = zpl_compat_ioctl,endif
};
dentry_operations：
typedef const struct dentry_operations dentry_operations_t;dentry_operations_t zpl_dops_snapdirs = { /*
- 仅在2.6.37及更高版本的内核中支持快照的自动挂载。
- 在此之前，ops->follow_link() 回调被用作触发挂载的hack。
- 结果的vfsmount然后被明确地移植到名称空间中。
- 虽然可能添加兼容代码来实现这一点，但需要相当小心。 */ .d_automount = zpl_snapdir_automount, .d_revalidate = zpl_snapdir_revalidate, };
dentry_operations_t zpl_dentry_operations = { .d_revalidate = zpl_revalidate, };
zfs io(zio) pipeline概述基本功能：
zio服务zfs的所有IO操作，负责将dva（数据虚拟地址）转换为硬件磁盘地址，通过vdevs提供动态压缩、去重、加密和校验等用户空间应用策略，实现镜像和raid z功能。
zfs文件写入过分分析：
zfs系统架构
-------------------system calls---------------------------
| |
kernel +-------------------+
+-----------| VFS |------------+
| File +-------------------+ |
| Systems | | |
| +-----------------------+ |
| | ZFS | | | |
| | +---------+ | |
| | | ZIO | | |
| | +---------+ | |
| | | vdevs | | |
| +------+---------+------+ |
| | | |
+--------------------------------------------+
| |
+----------------+
| block device |
+----------------+
| |
+------------+
| SCSI |
+------------+
| |
+------------+
| SAS |
+------------+
| |
V |
.-----------.
-----------
| disk |
-----------linux kernelsys_write：
当应用程序执行write函数时，会触发sys_write系统调用，具体的系统调用表可参考https://www.php.cn/link/1b7314ae41df37842b9d4e5e279caec1。
vfs_write：
vfs层提供统一的写接口，这里提供不同文件系统write的统一接口。
do_sync_write：
同步写接口。其中sys_write/vfs_write/do_sync_write是内核提供的抽象写接口，do_sync_write是内核4.x版本的函数，在5.x版本中是new_sync_write函数。不同版本的linux内核会导致部分系统函数存在差异。以下是参考linux kernel 5的内核代码分析：
// libc提供的write接口
SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf, size_t, count) {
return ksys_write(fd, buf, count);
}// write函数的系统调用
ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count) {
ret = vfs_write(f.file, buf, count, ppos);
return ret;
}
// 调用实际文件系统的file的write_iter函数，到这里基本完成kernel内核层面的系统调用，接下来就是实际zfs的写函数
static inline ssize_t call_write_iter(struct file file, struct kiocb kio, struct iov_iter iter) {
// struct file 的f_op是struct file_operations 指针，这个指针保存每个实际文件系统的文件操作的函数，这里需要查看zfs对应的file_opertions函数操作表
return file->f_op->write_iter(kio, iter);
}
zfs kernel：
zfs写数据过程分为两个阶段：open context和sync context。
open context阶段通过系统调用将数据从用户态拷贝到zfs的缓冲区，同时zfs将这些脏数据缓存在DMU中；sync context阶段判断脏数据是否超过4G，如果超过则通过zio批量将数据刷新到磁盘。DMU将数据写入ZIO，在ARC中缓存特定数据，并通知DSL层追踪空间使用。
第一阶段open context阶段是从zfs_write开始。zfs_write分为一个block的全部写和部分写；整块写首先针对块加锁，然后读取，在更改的新数据关联新的buffer；如果是部分写，首先也是读取操作，更改block中的部分内容，标记为脏页。
// z_node代表zfs中的inode，zfs_uio_t 是偏移量和长度
// 函数是经过省略的部分。
int zfs_write(znode_t zp, zfs_uio_t uio, int ioflag, cred_t cr) {
int error = 0;
ssize_t start_resid = zfs_uio_resid(uio);
ssize_t n = start_resid;
if (n == 0)
return (0);zfsvfs_t *zfsvfs = ZTOZSB(zp);
const uint64_t max_blksz = zfsvfs-youjiankuohaophpcnz_max_blksz;
if (zfs_uio_prefaultpages(MIN(n, max_blksz), uio)) {
ZFS_EXIT(zfsvfs);
return (SET_ERROR(EFAULT));
}
const rlim64_t limit = MAXOFFSET_T;
if (woff youjiankuohaophpcn= limit) {
zfs_rangelock_exit(lr);
ZFS_EXIT(zfsvfs);
return (SET_ERROR(EFBIG));
}
if (n youjiankuohaophpcn limit - woff)
n = limit - woff;
uint64_t end_size = MAX(zp-youjiankuohaophpcnz_size, woff + n);
zilog_t *zilog = zfsvfs-youjiankuohaophpcnz_log;
// 文件分割为多个文件chunk
while (n youjiankuohaophpcn 0) {
woff = zfs_uio_offset(uio);
arc_buf_t *abuf = NULL;
if (n youjiankuohaophpcn= max_blksz && woff youjiankuohaophpcn= zp-youjiankuohaophpcnz_size &&
P2PHASE(woff, max_blksz) == 0 &&
zp-youjiankuohaophpcnz_blksz == max_blksz) {
size_t cbytes;
abuf = dmu_request_arcbuf(sa_get_db(zp-youjiankuohaophpcnz_sa_hdl), max_blksz);
if ((error = zfs_uiocopy(abuf-youjiankuohaophpcnb_data, max_blksz, UIO_WRITE, uio, &cbytes))) {
dmu_return_arcbuf(abuf);
break;
}
ASSERT3S(cbytes, ==, max_blksz);
// 创建一个事务，表示准备更改操作，是否有空闲的空间
dmu_tx_t *tx = dmu_tx_create(zfsvfs-youjiankuohaophpcnz_os);
dmu_tx_hold_sa(tx, zp-youjiankuohaophpcnz_sa_hdl, B_FALSE);
dmu_buf_impl_t *db = (dmu_buf_impl_t *)sa_get_db(zp-youjiankuohaophpcnz_sa_hdl);
DB_DNODE_ENTER(db);
dmu_tx_hold_write_by_dnode(tx, DB_DNODE(db), woff, MIN(n, max_blksz));
// 等到喜爱一个可用的事务组，检查是否有足够空间和内存
error = dmu_tx_assign(tx, TXG_WAIT) {
dmu_tx_wait(tx) {
dmu_tx_delay(tx, dirty);
}
}
if (error) {
dmu_tx_abort(tx);
if (abuf != NULL)
dmu_return_arcbuf(abuf);
break;
}
if (lr-youjiankuohaophpcnlr_length == UINT64_MAX) {
uint64_t new_blksz;
if (zp-youjiankuohaophpcnz_blksz youjiankuohaophpcn max_blksz) {
new_blksz = MIN(end_size, zp-youjiankuohaophpcnz_blksz));
} else {
new_blksz = MIN(end_size, max_blksz);
}
zfs_grow_blocksize(zp, new_blksz, tx);
zfs_rangelock_reduce(lr, woff, n);
}
const ssize_t nbytes = MIN(n, max_blksz - P2PHASE(woff, max_blksz));
ssize_t tx_bytes;
if (abuf == NULL) {
tx_bytes = zfs_uio_resid(uio);
zfs_uio_fault_disable(uio, B_TRUE);
// 数据从uio写入到DMU
error = dmu_write_uio_dbuf(sa_get_db(zp-youjiankuohaophpcnz_sa_hdl), uio, nbytes, tx);
zfs_uio_fault_disable(uio, B_FALSE);ifdef linux
if (error == EFAULT) {
dmu_tx_commit(tx);
if (tx_bytes != zfs_uio_resid(uio))
n -= tx_bytes - zfs_uio_resid(uio);
if (zfs_uio_prefaultpages(MIN(n, max_blksz), uio)) {
break;
}
continue;
}
endif
if (error != 0) {
dmu_tx_commit(tx);
break;
}
tx_bytes -= zfs_uio_resid(uio);
} else {
error = dmu_assign_arcbuf_by_dbuf(sa_get_db(zp-youjiankuohaophpcnz_sa_hdl), woff, abuf, tx) {
dmu_assign_arcbuf_by_dnode(DB_DNODE(dbuf), offset, buf, tx) {
dbuf_assign_arcbuf(db, buf, tx) {
// 标记脏的dbuf
(void) dbuf_dirty(db, tx);
}
}
}
if (error != 0) {
dmu_return_arcbuf(abuf);
dmu_tx_commit(tx);
break;
}
}
error = sa_bulk_update(zp-youjiankuohaophpcnz_sa_hdl, bulk, count, tx);
// zfs log写入
zfs_log_write(zilog, tx, TX_WRITE, zp, woff, tx_bytes, ioflag, NULL, NULL);
dmu_tx_commit(tx);
}
if (ioflag & (O_SYNC | O_DSYNC) || zfsvfs-youjiankuohaophpcnz_os-youjiankuohaophpcnos_sync == ZFS_SYNC_ALWAYS)
// zfs intent log写入，更改数据写到磁盘之前必须先保证日志罗盘
zil_commit(zilog, zp-youjiankuohaophpcnz_id);
ZFS_EXIT(zfsvfs);
return (0);
}}
第二个阶段是sync context阶段，zfs会启动内核线程来同步事务组，然后进入dsl层的同步，在进入DMU层的同步，最后是ZIO的pipeline：
void txg_sync_start(dsl_pool_t dp) {
tx->tx_sync_thread = thread_create(NULL, 0, txg_sync_thread, 0) {
static void txg_sync_thread(void arg) {
for (;;) {
clock_t timeout = zfs_txg_timeout * hz;
spa_sync(spa, txg);
// 找到脏的数据集，call dsl_datasetsync->dmu_objset_sync->zio pipeline
txg_dispatch_callbacks(dp, txg);
}
}
}
} 
