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![David Howells](/assets/img/avatar_default.png)
Add a function to extract the pages from a user-space supplied iterator (UBUF- or IOVEC-type) into a BVEC-type iterator, retaining the pages by getting a pin on them (as FOLL_PIN) as we go. This is useful in three situations: (1) A userspace thread may have a sibling that unmaps or remaps the process's VM during the operation, changing the assignment of the pages and potentially causing an error. Retaining the pages keeps some pages around, even if this occurs; futher, we find out at the point of extraction if EFAULT is going to be incurred. (2) Pages might get swapped out/discarded if not retained, so we want to retain them to avoid the reload causing a deadlock due to a DIO from/to an mmapped region on the same file. (3) The iterator may get passed to sendmsg() by the filesystem. If a fault occurs, we may get a short write to a TCP stream that's then tricky to recover from. We don't deal with other types of iterator here, leaving it to other mechanisms to retain the pages (eg. PG_locked, PG_writeback and the pipe lock). Signed-off-by: David Howells <dhowells@redhat.com> cc: Jeff Layton <jlayton@kernel.org> cc: Steve French <sfrench@samba.org> cc: Shyam Prasad N <nspmangalore@gmail.com> cc: Rohith Surabattula <rohiths.msft@gmail.com> cc: linux-cachefs@redhat.com cc: linux-cifs@vger.kernel.org cc: linux-fsdevel@vger.kernel.org Signed-off-by: Steve French <stfrench@microsoft.com>
12 lines
191 B
Makefile
12 lines
191 B
Makefile
# SPDX-License-Identifier: GPL-2.0
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netfs-y := \
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buffered_read.o \
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io.o \
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iterator.o \
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main.o \
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objects.o
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netfs-$(CONFIG_NETFS_STATS) += stats.o
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obj-$(CONFIG_NETFS_SUPPORT) := netfs.o
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