- 14 Mar, 2022 40 commits
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Qu Wenruo authored
[BUG] There is a bug report that a bitflip in the transid part of an extent buffer makes btrfs to reject certain tree blocks: BTRFS error (device dm-0): parent transid verify failed on 1382301696 wanted 262166 found 22 [CAUSE] Note the failed transid check, hex(262166) = 0x40016, while hex(22) = 0x16. It's an obvious bitflip. Furthermore, the reporter also confirmed the bitflip is from the hardware, so it's a real hardware caused bitflip, and such problem can not be detected by the existing tree-checker framework. As tree-checker can only verify the content inside one tree block, while generation of a tree block can only be verified against its parent. So such problem remain undetected. [FIX] Although tree-checker can not verify it at write-time, we still have a quick (but not the most accurate) way to catch such obvious corruption. Function csum_one_extent_buffer() is called before we submit metadata write. Thus it means, all the extent buffer passed in should be dirty tree blocks, and should be newer than last committed transaction. Using that we can catch the above bitflip. Although it's not a perfect solution, as if the corrupted generation is higher than the correct value, we have no way to catch it at all. Reported-by:
Christoph Anton Mitterer <calestyo@scientia.org> Link: https://lore.kernel.org/linux-btrfs/2dfcbc130c55cc6fd067b93752e90bd2b079baca.camel@scientia.org/ CC: stable@vger.kernel.org # 5.15+ Signed-off-by:
Qu Wenruo <wqu@sus,ree.com> Reviewed-by:
David Sterba <dsterba@suse.com> Signed-off-by:
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Qu Wenruo authored
There is one oddball error handling of btrfs_read_buffer(): ret = btrfs_read_buffer(tmp, gen, parent_level - 1, &first_key); if (!ret) { *eb_ret = tmp; return 0; } free_extent_buffer(tmp); btrfs_release_path(p); return -EIO; While all other call sites check the error first. Unify the behavior. Signed-off-by:Qu Wenruo <wqu@suse.com> Reviewed-by:
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Qu Wenruo authored
We had an error handling pattern for read_tree_block() like this: eb = read_tree_block(); if (IS_ERR(eb)) { /* * Handling error here * Normally ended up with return or goto out. */ } else if (!extent_buffer_uptodate(eb)) { /* * Different error handling here * Normally also ended up with return or goto out; */ } This is fine, but if we want to add extra check for each read_tree_block(), the existing if-else-if is not that expandable and will take reader some seconds to figure out there is no extra branch. Here we change it to a more common way, without the extra else: eb = read_tree_block(); if (IS_ERR(eb)) { /* * Handling error here */ return eb or goto out; } if (!extent_buffer_uptodate(eb)) { /* * Different error handling here */ return eb or goto out; } This also removes some oddball call sites which uses some creative way to check error. Signed-off-by: -
Josef Bacik authored
__btrfs_free_extent() does all of the hard work of updating the extent ref items, and then at the end if we dropped the extent completely it does the cleanup accounting work. We're going to only want to do that work for metadata with extent tree v2, so extract this bit into its own helper. Signed-off-by:
Josef Bacik <josef@toxicpanda.com> Reviewed-by:
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Josef Bacik authored
This is a remnant of the work I did for qgroups a long time ago to only run for a block when we had dropped the last ref. We haven't done that for years, but the code remains. Drop this remnant. Signed-off-by:
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Josef Bacik authored
We duplicate this logic for both data and metadata, at this point we've already done our type specific extent root operations, this is just doing the accounting and removing the space from the free space tree. Extract this common logic out into a helper. Signed-off-by:
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Josef Bacik authored
Switch this to an ASSERT() and return the error in the normal case. Signed-off-by:
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Filipe Manana authored
During log replay there is this pattern of running delayed items after every inode unlink. To avoid repeating this several times, move the logic into an helper function and use it instead of calling btrfs_unlink_inode() followed by btrfs_run_delayed_items(). Signed-off-by:
Filipe Manana <fdmanana@suse.com> Signed-off-by:
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Niels Dossche authored
bytes_pinned is always accessed under space_info->lock, except in btrfs_preempt_reclaim_metadata_space, however the other members are accessed under that lock. The reserved member of the rsv's are also partially accessed under a lock and partially not. Move all these accesses into the same lock to ensure consistency. This could potentially race and lead to a flush instead of a commit but it's not a big problem as it's only for preemptive flush. CC: stable@vger.kernel.org # 5.15+ Reviewed-by:
Johannes Thumshirn <johannes.thumshirn@wdc.com> Reviewed-by:
Niels Dossche <niels.dossche@ugent.be> Signed-off-by:
Niels Dossche <dossche.niels@gmail.com> Reviewed-by:
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Naohiro Aota authored
There is a hung_task issue with running generic/068 on an SMR device. The hang occurs while a process is trying to thaw the filesystem. The process is trying to take sb->s_umount to thaw the FS. The lock is held by fsstress, which calls btrfs_sync_fs() and is waiting for an ordered extent to finish. However, as the FS is frozen, the ordered extents never finish. Having an ordered extent while the FS is frozen is the root cause of the hang. The ordered extent is initiated from btrfs_relocate_chunk() which is called from btrfs_reclaim_bgs_work(). This commit adds sb_*_write() around btrfs_relocate_chunk() call site. For the usual "btrfs balance" command, we already call it with mnt_want_file() in btrfs_ioctl_balance(). Fixes: 18bb8bbf ("btrfs: zoned: automatically reclaim zones") CC: stable@vger.kernel.org # 5.13+ Link: https://github.com/naota/linux/issues/56Reviewed-by:
Naohiro Aota <naohiro.aota@wdc.com> Reviewed-by:
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Josef Bacik authored
Currently we disallow reflink and dedupe if the two files aren't on the same vfsmount. However we really only need to disallow it if they're not on the same super block. It is very common for btrfs to have a main subvolume that is mounted and then different subvolumes mounted at different locations. It's allowed to reflink between these volumes, but the vfsmount check disallows this. Instead fix dedupe to check for the same superblock, and simply remove the vfsmount check for reflink as it already does the superblock check. Reviewed-by:
Darrick J. Wong <djwong@kernel.org> Reviewed-by:
Nikolay Borisov <nborisov@suse.com> Signed-off-by:
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Josef Bacik authored
The sb check is already done in do_clone_file_range, and the mnt check (which will hopefully go away in a subsequent patch) is done in ioctl_file_clone(). Remove the check in our code and put an ASSERT() to make sure it doesn't change underneath us. Reviewed-by:
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Josef Bacik authored
We don't need a root here, we just need the btrfs_fs_info, we can just get the specific roots we need from fs_info. Reviewed-by:
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Josef Bacik authored
We're passing a root around here, but we only really need the fs_info, so fix up btrfs_clean_one_deleted_snapshot() to take an fs_info instead, and then fix up all the callers appropriately. Reviewed-by:
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Sweet Tea Dorminy authored
When a filesystem goes read-only due to an error, multiple errors tend to be reported, some of which are knock-on failures. Logging fs_states, in btrfs_handle_fs_error() and btrfs_printk() helps distinguish the first error from subsequent messages which may only exist due to an error state. Under the new format, most initial errors will look like: `BTRFS: error (device loop0) in ...` while subsequent errors will begin with: `error (device loop0: state E) in ...` An initial transaction abort error will look like `error (device loop0: state A) in ...` and subsequent messages will contain `(device loop0: state EA) in ...` In addition to the error states we can also print other states that are temporary, like remounting, device replace, or indicate a global state that may affect functionality. Now implemented: E - filesystem error detected A - transaction aborted L - log tree errors M - remounting in progress R - device replace in progress C - data checksums not verified (mounted with ignoredatacsums) Signed-off-by:
Sweet Tea Dorminy <sweettea-kernel@dorminy.me> Reviewed-by:
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Filipe Manana authored
Smatch complains about a possible dereference of a pointer that was not initialized: CC [M] fs/btrfs/reflink.o CHECK fs/btrfs/reflink.c fs/btrfs/reflink.c:533 btrfs_clone() error: potentially dereferencing uninitialized 'trans'. This is because we are not dealing with the case where the type of a file extent has an unexpected value (not regular, not prealloc and not inline), in which case the transaction handle pointer is not initialized. Such unexpected type should be impossible, except in case of some memory corruption caused either by bad hardware or some software bug causing something like a buffer overrun. So ASSERT that if the extent type is neither regular nor prealloc, then it must be inline. Bail out with -EUCLEAN and a warning in case it is not. This silences smatch. Signed-off-by: -
Filipe Manana authored
When reflinking an inline extent, we assert that its file offset is 0 and that its uncompressed length is not greater than the sector size. We then return an error if one of those conditions is not satisfied. However we use a return statement, which results in returning from btrfs_clone() without freeing the path and buffer that were allocated before, as well as not clearing the flag BTRFS_INODE_NO_DELALLOC_FLUSH for the destination inode. Fix that by jumping to the 'out' label instead, and also add a WARN_ON() for each condition so that in case assertions are disabled, we get to known which of the unexpected conditions triggered the error. Fixes: a61e1e0d ("Btrfs: simplify inline extent handling when doing reflinks") Signed-off-by:
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Filipe Manana authored
When an inode has a last_reflink_trans matching the current transaction, we have to take special care when logging its checksums in order to avoid getting checksum items with overlapping ranges in a log tree, which could result in missing checksums after log replay (more on that in the changelogs of commit 40e046ac ("Btrfs: fix missing data checksums after replaying a log tree") and commit e289f03e ("btrfs: fix corrupt log due to concurrent fsync of inodes with shared extents")). We also need to make sure a full fsync will copy all old file extent items it finds in modified leaves, because they might have been copied from some other inode. However once we fsync an inode, we don't need to keep paying the price of that extra special care in future fsyncs done in the same transaction, unless the inode is used for another reflink operation or the full sync flag is set on it (truncate, failure to allocate extent maps for holes, and other exceptional and infrequent cases). So after we fsync an inode reset its last_unlink_trans to zero. In case another reflink happens, we continue to update the last_reflink_trans of the inode, just as before. Also set last_reflink_trans to the generation of the last transaction that modified the inode whenever we need to set the full sync flag on the inode, just like when we need to load an inode from disk after eviction. Signed-off-by:
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Filipe Manana authored
Doing a full fsync may require processing many leaves of metadata, which can take some time and result in a task monopolizing a cpu for too long. So add a cond_resched() after processing a leaf when doing a full fsync, while not holding any locks on any tree (a subvolume or a log tree). Signed-off-by:
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Filipe Manana authored
When doing a full fsync, at copy_items(), we iterate over all extents and then collect their checksums into a list. After copying all the extents to the log tree, we then log all the previously collected checksums. Before the previous patch in the series (subject "btrfs: stop copying old file extents when doing a full fsync"), we had to do it this way, because while we were iterating over the items in the leaf of the subvolume tree, we were holding a write lock on a leaf of the log tree, so logging the checksums for an extent right after we collected them could result in a deadlock, in case the checksum items ended up in the same leaf. However after the previous patch in the series we now do a first iteration over all the items in the leaf of the subvolume tree before locking a path in the log tree, so we can now log the checksums right after we have obtained them. This avoids holding in memory all checksums for all extents in the leaf while copying items from the source leaf to the log tree. The amount of memory used to hold all checksums of the extents in a leaf can be significant. For example if a leaf has 200 file extent items referring to 1M extents, using the default crc32c checksums, would result in using over 200K of memory (not accounting for the extra overhead of struct btrfs_ordered_sum), with smaller or less extents it would be less, but it could be much more with more extents per leaf and/or much larger extents. So change copy_items() to log the checksums for an extent after looking them up, and then free their memory, as they are no longer necessary. Signed-off-by:
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Filipe Manana authored
When logging an inode in full sync mode, we go over every leaf that was modified in the current transaction and has items associated to our inode, and then copy all those items into the log tree. This includes copying file extent items that were created and added to the inode in past transactions, which is useless and only makes use more leaf space in the log tree. It's common to have a file with many file extent items spanning many leaves where only a few file extent items are new and need to be logged, and in such case we log all the file extent items we find in the modified leaves. So change the full sync behaviour to skip over file extent items that are not needed. Those are the ones that match the following criteria: 1) Have a generation older than the current transaction and the inode was not a target of a reflink operation, as that can copy file extent items from a past generation from some other inode into our inode, so we have to log them; 2) Start at an offset within i_size - we must log anything at or beyond i_size, otherwise we would lose prealloc extents after log replay. The following script exercises a scenario where this happens, and it's somehow close enough to what happened often on a SQL Server workload which I had to debug sometime ago to fix an issue where a pattern of writes to prealloc extents and fsync resulted in fsync failing with -EIO (that was commit ea7036de ("btrfs: fix fsync failure and transaction abort after writes to prealloc extents")). In that particular case, we had large files that had random writes and were often truncated, which made the next fsync be a full sync. $ cat test.sh #!/bin/bash DEV=/dev/sdi MNT=/mnt/sdi MKFS_OPTIONS="-O no-holes -R free-space-tree" MOUNT_OPTIONS="-o ssd" FILE_SIZE=$((1 * 1024 * 1024 * 1024)) # 1G # FILE_SIZE=$((2 * 1024 * 1024 * 1024)) # 2G # FILE_SIZE=$((512 * 1024 * 1024)) # 512M mkfs.btrfs -f $MKFS_OPTIONS $DEV mount $MOUNT_OPTIONS $DEV $MNT # Create a file with many extents. Use direct IO to make it faster # to create the file - using buffered IO we would have to fsync # after each write (terribly slow). echo "Creating file with $((FILE_SIZE / 4096)) extents of 4K each..." xfs_io -f -d -c "pwrite -b 4K 0 $FILE_SIZE" $MNT/foobar # Commit the transaction, so every extent after this is from an # old generation. sync # Now rewrite only a few extents, which are all far spread apart from # each other (e.g. 1G / 32M = 32 extents). # After this only a few extents have a new generation, while all other # ones have an old generation. echo "Rewriting $((FILE_SIZE / (32 * 1024 * 1024))) extents..." for ((i = 0; i < $FILE_SIZE; i += $((32 * 1024 * 1024)))); do xfs_io -c "pwrite $i 4K" $MNT/foobar >/dev/null done # Fsync, the inode logged in full sync mode since it was never fsynced # before. echo "Fsyncing file..." xfs_io -c "fsync" $MNT/foobar umount $MNT And the following bpftrace program was running when executing the test script: $ cat bpf-script.sh #!/usr/bin/bpftrace k:btrfs_log_inode { @start_log_inode[tid] = nsecs; } kr:btrfs_log_inode /@start_log_inode[tid]/ { @log_inode_dur[tid] = (nsecs - @start_log_inode[tid]) / 1000; delete(@start_log_inode[tid]); } k:btrfs_sync_log { @start_sync_log[tid] = nsecs; } kr:btrfs_sync_log /@start_sync_log[tid]/ { $sync_log_dur = (nsecs - @start_sync_log[tid]) / 1000; printf("btrfs_log_inode() took %llu us\n", @log_inode_dur[tid]); printf("btrfs_sync_log() took %llu us\n", $sync_log_dur); delete(@start_sync_log[tid]); delete(@log_inode_dur[tid]); exit(); } With 512M test file, before this patch: btrfs_log_inode() took 15218 us btrfs_sync_log() took 1328 us Log tree has 17 leaves and 1 node, its total size is 294912 bytes. With 512M test file, after this patch: btrfs_log_inode() took 14760 us btrfs_sync_log() took 588 us Log tree has a single leaf, its total size is 16K. With 1G test file, before this patch: btrfs_log_inode() took 27301 us btrfs_sync_log() took 1767 us Log tree has 33 leaves and 1 node, its total size is 557056 bytes. With 1G test file, after this patch: btrfs_log_inode() took 26166 us btrfs_sync_log() took 593 us Log tree has a single leaf, its total size is 16K With 2G test file, before this patch: btrfs_log_inode() took 50892 us btrfs_sync_log() took 3127 us Log tree has 65 leaves and 1 node, its total size is 1081344 bytes. With 2G test file, after this patch: btrfs_log_inode() took 50126 us btrfs_sync_log() took 586 us Log tree has a single leaf, its total size is 16K. Signed-off-by:
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Josef Bacik authored
The submit helper will always run bio_endio() on the bio if it fails to submit, so cleaning up the bio just leads to a variety of use-after-free and NULL pointer dereference bugs because we race with the endio function that is cleaning up the bio. Instead just return BLK_STS_OK as the repair function has to continue to process the rest of the pages, and the endio for the repair bio will do the appropriate cleanup for the page that it was given. Reviewed-by:
Boris Burkov <boris@bur.io> Signed-off-by:
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Josef Bacik authored
If we fail to submit a bio for whatever reason, we may not have setup a mirror_num for that bio. This means we shouldn't try to do the repair workflow, if we do we'll hit an BUG_ON(!failrec->this_mirror) in clean_io_failure. Instead simply skip the repair workflow if we have no mirror set, and add an assert to btrfs_check_repairable() to make it easier to catch what is happening in the future. Reviewed-by:
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Josef Bacik authored
I hit some weird panics while fixing up the error handling from btrfs_lookup_bio_sums(). Turns out the compression path will complete the bio we use if we set up any of the compression bios and then return an error, and then btrfs_submit_data_bio() will also call bio_endio() on the bio. Fix this by making btrfs_submit_compressed_read() responsible for calling bio_endio() on the bio if there are any errors. Currently it was only doing it if we created the compression bios, otherwise it was depending on btrfs_submit_data_bio() to do the right thing. This creates the above problem, so fix up btrfs_submit_compressed_read() to always call bio_endio() in case of an error, and then simply return from btrfs_submit_data_bio() if we had to call btrfs_submit_compressed_read(). Signed-off-by:
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Josef Bacik authored
Right now we just have a binary "errors" flag, so any error we get on the compressed bio's gets translated to EIO. This isn't necessarily a bad thing, but if we get an ENOMEM it may be nice to know that's what happened instead of an EIO. Track our errors as a blk_status_t, and do the appropriate setting of the errors accordingly. Signed-off-by:
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Josef Bacik authored
This bio is usually one of the compressed bio's, and we don't actually need it in this function, so remove the argument and stop passing it around. Reviewed-by:
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Josef Bacik authored
Commit c09abff8 ("btrfs: cloned bios must not be iterated by bio_for_each_segment_all") added ASSERT()'s to make sure we weren't calling bio_for_each_segment_all() on a RAID5/6 bio. However it was checking the bio that the compression code passed in, not the cb->orig_bio that we actually iterate over, so adjust this ASSERT() to check the correct bio. Reviewed-by:
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Josef Bacik authored
Currently any error we get while trying to lookup csums during reads shows up as a missing csum, and then on the read completion side we print an error saying there was a csum mismatch and we increase the device corruption count. However we could have gotten an EIO from the lookup. We could also be inside of a memory constrained container and gotten a ENOMEM while trying to do the read. In either case we don't want to make this look like a file system corruption problem, we want to make it look like the actual error it is. Capture any negative value, convert it to the appropriate blk_status_t, free the csum array if we have one and bail. Note: a possible improvement would be to make the relocation code look up the owning inode and see if it's marked as NODATASUM and set EXTENT_NODATASUM there, that way if there's corruption and there isn't a checksum when we want it we can fail here rather than later. Signed-off-by:
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Josef Bacik authored
We can either fail to find a csum entry at all and return -ENOENT, or we can find a range that is close, but return -EFBIG. In essence these both mean the same thing when we are doing a lookup for a csum in an existing range, we didn't find a csum. We want to treat both of these errors the same way, complain loudly that there wasn't a csum. This currently happens anyway because we do count = search_csum_tree(); if (count <= 0) { // reloc and error handling } However it forces us to incorrectly treat EIO or ENOMEM errors as on disk corruption. Fix this by returning 0 if we get either -ENOENT or -EFBIG from btrfs_lookup_csum() so we can do proper error handling. Reviewed-by: -
Omar Sandoval authored
The implementation resembles direct I/O: we have to flush any ordered extents, invalidate the page cache, and do the io tree/delalloc/extent map/ordered extent dance. From there, we can reuse the compression code with a minor modification to distinguish the write from writeback. This also creates inline extents when possible. Signed-off-by:
Omar Sandoval <osandov@fb.com> Signed-off-by:
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Omar Sandoval authored
There are 4 main cases: 1. Inline extents: we copy the data straight out of the extent buffer. 2. Hole/preallocated extents: we fill in zeroes. 3. Regular, uncompressed extents: we read the sectors we need directly from disk. 4. Regular, compressed extents: we read the entire compressed extent from disk and indicate what subset of the decompressed extent is in the file. This initial implementation simplifies a few things that can be improved in the future: - Cases 1, 3, and 4 allocate temporary memory to read into before copying out to userspace. - We don't do read repair, because it turns out that read repair is currently broken for compressed data. - We hold the inode lock during the operation. Note that we don't need to hold the mmap lock. We may race with btrfs_page_mkwrite() and read the old data from before the page was dirtied: btrfs_page_mkwrite btrfs_encoded_read --------------------------------------------------- (enter) (enter) btrfs_wait_ordered_range lock_extent_bits btrfs_page_set_dirty unlock_extent_cached (exit) lock_extent_bits read extent (dirty page hasn't been flushed, so this is the old data) unlock_extent_cached (exit) we read the old data from before the page was dirtied. But, that's true even if we were to hold the mmap lock: btrfs_page_mkwrite btrfs_encoded_read ------------------------------------------------------------------- (enter) (enter) btrfs_inode_lock(BTRFS_ILOCK_MMAP) down_read(i_mmap_lock) (blocked) btrfs_wait_ordered_range lock_extent_bits read extent (page hasn't been dirtied, so this is the old data) unlock_extent_cached btrfs_inode_unlock(BTRFS_ILOCK_MMAP) down_read(i_mmap_lock) returns lock_extent_bits btrfs_page_set_dirty unlock_extent_cached In other words, this is inherently racy, so it's fine that we return the old data in this tiny window. Signed-off-by: -
Omar Sandoval authored
In order to allow sending and receiving compressed data without decompressing it, we need an interface to write pre-compressed data directly to the filesystem and the matching interface to read compressed data without decompressing it. This adds the definitions for ioctls to do that and detailed explanations of how to use them. Reviewed-by:
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Omar Sandoval authored
Currently, an inline extent is always created after i_size is extended from btrfs_dirty_pages(). However, for encoded writes, we only want to update i_size after we successfully created the inline extent. Add an update_i_size parameter to cow_file_range_inline() and insert_inline_extent() and pass in the size of the extent rather than determining it from i_size. Reviewed-by:
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Omar Sandoval authored
The start parameter to cow_file_range_inline() (and insert_inline_extent()) is always 0, so get rid of it and simplify the logic in those two functions. Pass btrfs_inode to insert_inline_extent() and remove the redundant root parameter. Also document the requirements for creating an inline extent. No functional change. Signed-off-by:
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Omar Sandoval authored
Currently, we always reserve the same extent size in the file and extent size on disk for delalloc because the former is the worst case for the latter. For BTRFS_IOC_ENCODED_WRITE writes, we know the exact size of the extent on disk, which may be less than or greater than (for bookends) the size in the file. Add a disk_num_bytes parameter to btrfs_delalloc_reserve_metadata() so that we can reserve the correct amount of csum bytes. No functional change. Reviewed-by:
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Omar Sandoval authored
Currently, we only create ordered extents when ram_bytes == num_bytes and offset == 0. However, BTRFS_IOC_ENCODED_WRITE writes may create extents which only refer to a subset of the full unencoded extent, so we need to plumb these fields through the ordered extent infrastructure and pass them down to insert_reserved_file_extent(). Since we're changing the btrfs_add_ordered_extent* signature, let's get rid of the trivial wrappers and add a kernel-doc. Reviewed-by:
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Omar Sandoval authored
btrfs_csum_one_bio() loops over each filesystem block in the bio while keeping a cursor of its current logical position in the file in order to look up the ordered extent to add the checksums to. However, this doesn't make much sense for compressed extents, as a sector on disk does not correspond to a sector of decompressed file data. It happens to work because: 1) the compressed bio always covers one ordered extent 2) the size of the bio is always less than the size of the ordered extent However, the second point will not always be true for encoded writes. Let's add a boolean parameter to btrfs_csum_one_bio() to indicate that it can assume that the bio only covers one ordered extent. Since we're already changing the signature, let's get rid of the contig parameter and make it implied by the offset parameter, similar to the change we recently made to btrfs_lookup_bio_sums(). Additionally, let's rename nr_sectors to blockcount to make it clear that it's the number of filesystem blocks, not the number of 512-byte sectors. Reviewed-by:
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Omar Sandoval authored
Encoded I/O in Btrfs needs to check a write with a given logical size without an iov_iter that matches that size (because the iov_iter we have is for the compressed data). So, factor out the parts of generic_write_check() that don't need an iov_iter into a new generic_write_checks_count() function and export that. Reviewed-by:
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Omar Sandoval authored
I'm adding btrfs ioctls to read and write compressed data, and rather than duplicating the checks in rw_verify_area(), let's just export it. Reviewed-by:
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Sidong Yang authored
These comments are old, outdated and not very specific. It seems that it doesn't help to inspire anybody to work on that. So we remove them. Reviewed-by:
Sidong Yang <realwakka@gmail.com> Reviewed-by:
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