1b8ab8159e
Copy the inode size and blocks from one inode to another correctly on 32-bit systems with CONFIG_SMP, CONFIG_PREEMPT, or CONFIG_LBDAF. Use proper inode spinlocks only when i_size/i_blocks cannot fit in one 32-bit word. Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
80 lines
2.7 KiB
C
80 lines
2.7 KiB
C
#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/fs_stack.h>
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/* does _NOT_ require i_mutex to be held.
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*
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* This function cannot be inlined since i_size_{read,write} is rather
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* heavy-weight on 32-bit systems
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*/
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void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
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{
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loff_t i_size;
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blkcnt_t i_blocks;
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/*
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* i_size_read() includes its own seqlocking and protection from
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* preemption (see include/linux/fs.h): we need nothing extra for
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* that here, and prefer to avoid nesting locks than attempt to keep
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* i_size and i_blocks in sync together.
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*/
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i_size = i_size_read(src);
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/*
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* But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to
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* keep the two halves of i_blocks in sync despite SMP or PREEMPT -
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* though stat's generic_fillattr() doesn't bother, and we won't be
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* applying quotas (where i_blocks does become important) at the
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* upper level.
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*
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* We don't actually know what locking is used at the lower level;
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* but if it's a filesystem that supports quotas, it will be using
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* i_lock as in inode_add_bytes(). tmpfs uses other locking, and
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* its 32-bit is (just) able to exceed 2TB i_size with the aid of
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* holes; but its i_blocks cannot carry into the upper long without
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* almost 2TB swap - let's ignore that case.
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*/
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if (sizeof(i_blocks) > sizeof(long))
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spin_lock(&src->i_lock);
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i_blocks = src->i_blocks;
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if (sizeof(i_blocks) > sizeof(long))
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spin_unlock(&src->i_lock);
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/*
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* If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
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* fsstack_copy_inode_size() to hold some lock around
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* i_size_write(), otherwise i_size_read() may spin forever (see
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* include/linux/fs.h). We don't necessarily hold i_mutex when this
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* is called, so take i_lock for that case.
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*
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* And if CONFIG_LBADF (on 32-bit), continue our effort to keep the
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* two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
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* for that case too, and do both at once by combining the tests.
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*
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* There is none of this locking overhead in the 64-bit case.
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*/
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if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
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spin_lock(&dst->i_lock);
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i_size_write(dst, i_size);
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dst->i_blocks = i_blocks;
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if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
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spin_unlock(&dst->i_lock);
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}
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EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
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/* copy all attributes */
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void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
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{
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dest->i_mode = src->i_mode;
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dest->i_uid = src->i_uid;
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dest->i_gid = src->i_gid;
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dest->i_rdev = src->i_rdev;
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dest->i_atime = src->i_atime;
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dest->i_mtime = src->i_mtime;
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dest->i_ctime = src->i_ctime;
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dest->i_blkbits = src->i_blkbits;
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dest->i_flags = src->i_flags;
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dest->i_nlink = src->i_nlink;
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}
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EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);
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